William, most of the books reliably dealing with the subject are long out of print. The majority were printed from the late 1800's to the mid-1900's....in Great Britain. I know of no recent publications. I am fortunate to have a few on disc and a couple of originals left to me by family members.
Just so you will know, here's a bibliography from which the compendium was compiled: (not all of the below deal with the Picts)
Akermana John Yonge, "Remains of Pagan Saxondom". London, 1860.
Alexander, William L., "The Ancient British Church". London, 1889
Anderson, Alan Orr, "Early Sources of Scottish History". Edinburgh,
1922.
Angus, S., "The Mystery Religions and Christianity". London, 1928.
Arnold, Channing and F. J. T. Frost, "The American Egypt. A Record of
Travel in Yucatan". London, 1909.
Avebury, Lord, "Pre-Historic Times". London, 1900.
Avery, Catherine B., Ed., "The New Century Classical Handbook". New
York, 1962.
Ayer, Joseph Cullen, Jr., "A Source Book for Ancient Church History".
New York, 1941.
Baikie, James, "The Sea Kings of Crete". London, 1926.
Bancroft, Hubert Howe, "The Native Races of the Pacific States of North
America". 5 vol. New York, 1875.
Berington, Joseph, "A Literary History of the Middle Ages". London,
1814.
Bingham, Hiram, "Lost City of the Incas". London, 1951.
Bingham, Joseph, "The Antiquities of the Christian Church". 2 vol.
London, 1920.
Bradley, Henry, "The Story of the Goths". London, 1891.
Bradley, R. N., "Malta and the Mediterranean Race". London, 1912.
Brion, Marcel, "The World of Archaeology India, China, and America".
London, 1959.
Browne, G. F., "The Church In These Islands Before Augustine". New
York, 1897.
Browne, James, "A History of the Highlands and of the Highland Clans".
Edinburgh, 1852.
Browne, James, "The History of Scotland, its Highlands, Regiments, and
Clans". 8 vol. London, 1909.
Buckle, Henry Thomas, "Introduction to the Civilization in England".
New York, 1904.
Burton, John Hill, "The History of Scotland". 8 vol. Edinburgh, 1897.
Camden, William, "Remains Concerning Britain". London 1674.
Cameron, Mary Lovett, "Old Etruria and Modern Tuscany". London, 1909.
Cano, Benito, "Coronica General De Espana". Madrid, 1791.
Catrou and Rouille, "The Roman History". 6 vol. London 1728.
Cave, William, "Antiquitates Apostolicae -- The History of the
Apostles". London, 1684.
Childe, V Gordon, "The Prehistory of Scotland". London 1935.
Churton, Edward, "The Early English Church". London.
Clark, Grahame, "Prehistoric England". London, 1962.
Cobern, Camden M., "The New Archaeological Discoveries and Their
Bearing on the New Testament". London, 1918.
Coulton, G. G., "Medieval Panorama". Cambridge, 1949.
Crichton, Andrew, "Scandinavia, Ancient and Modern". 2 vol. New York,
1841.
Cunnington, M. E., "An Introduction to the Archaeology of Wiltshire".
1949.
de Bourbourg, LeAbbe Brasseur, "Histoire Des Nations Civilisees Du
Mexique et de L'Amerique -- Centrale". Paris, 1857.
de Hirsch-Davies, J. E., "A Popular History of the Church in Wales".
London, 1912.
de Laet, S. J., "The Low Countries". London, 1958.
de Leon, Pedro de Cieza, Trans. Victor W. von Hagen, "The Incas".
Oklahoma, 1959.
de Nadaillac, "Prehistoric America". New York, 1884.
de Ocampo, Battasar, "History of the Incas". Cambridge, 1907.
de Paor, M. snd D., "Early Christian Ireland". London, 1959.
de Pufendorf, Baron Samuel, "Histoire de Suede". Amsterdam, 1730.
de Sahagun, Bernardino, "A History of Ancient Mexico". 1932.
Elton, Oliver, translator, "The Danish History of Saxo Grammaticus".
London, 1894.
Evans, J. D., "Malta". London, 1959.
Evans, John, "The Ancient Stone Implements, Weapons and Ornaments of
Great Britain". New York, 1872.
Ferrero, Guglielmo, "Characters and Events of Roman History". New York,
1909.
Foster, J. W., "Pre-Historic Races of the United States of America".
Chicago, 1878.
Gallenkamp, Charles, "Maya -- The Riddle and Rediscovery of a Lost
Civilization". New York, 1959.
Geddes, Michael, "The Church History of Ethiopia". London, 1694.
Geoffrey of Monmouth, "History of the Kings of Britain". New York,
1958.
Gilles, J. A., "Six Old English Chronicles", including Ethelwerd's
chronlele, Asser's Life of Alfred, Geoffrey of Monmouth's British
History, Gildas and Nennius. London, 1908.
Gjerset, Knut, "History of the Norwegian People". New York, 1932.
Gregg, William H., "Controversial Issues in Scottish History". London,
1910.
Guest, Edwln, "Origines Celticae". 2 vol. London, 1883.
Harvey, G. E., "History of Burma". London, 1925.
Heyerdahl, Thor., "American Indians in the Pacific". Stockholm, 1952.
Holmes, T. Rice, "Ancient Britain and the Invasions of Julius Caesar".
London, 1907.
Hubert, Henri, "The Rise of the Celts". London, 1934.
Johnson, Walter, "Byways in British Archaeology". Cambridge, 1912.
Jones, Inigo, "Stone-heng". London, 1655.
Kadar, Zoltan, "Die Kleinasiatisch -- Syrischen Kulte Zur Romerzeit in
Ungarn". Leiden, 1962.
Kelly, Matthew, Editor and Translator, "Cambrensis Eversus". Dublin,
1848.
Kephart, Calvin, "Races of Mankind, Their Origin and Migration".
London, 1961.
Krickeberg, Walter, "Altmexikanische Kulturen". Berlin, 1956.
Laing, Samuel, Translator, "The Kings of Norway, or The Heimskringla".
London, 1844.
Lebreton, Jules and Jacques Zeilkr, "The History of the Primitive
Church". 3 vol. London, 1949.
Lhoyd, H., "The Historie of Cambria". 1584.
Lothrop, Samuel (and staff), "Essays in Pre-Columbian Art and
Archaeology". Cambridge, Mass., 1961.
MacAirt, Sean., "The Annals of Inisfallen". Dublin, 1951.
MacCullouch, J. A., "The Religion of the Ancient Celts". Edinburgh,
1911.
MacDonald, E., "A Gaelic Dictionary", 3 vol. Scotland, 1902.
MacKenzie, Donald A., "Ancient Man in Britain". London, 1923.
MacRitchie, David, "The Testimony of Tradition". London, 1890
Markham, Sir Clements, "The Incas of Peru". London, 1910.
Mason, J. Alden, "The Ancient Civilizations of Peru". Edinburgh, 1951
Means, Philip A., "Ancient Civilizations of the Andes". New York, 1931.
Menzel, Wolfgang, "Germany From the Earliest Period". New York, 1899.
Merryweather, F. Somner, "Bibliomania in the Middle Ages". London,
1933.
Mierow, Charles Christopher, "The Gothic History of Jordanes". New
York, 1960.
Mueller, F. Max, "Chips from a German Workshop", Vol. 3. London, 1870.
Nicephoros, "Ecclesiasticae Historiae", Vol. 1. 1630.
"Norroena The History and Romance of Northern Europe. 1906, Saxo
Edition.
Olrik, Axel; Hollander, Lee M., Translator, "The Heroic Legends of
Denmark". New York, 1919.
O'Rahilly, Thomas F., "Early Irish History and Mythology". Dublin,
1946.
Pallottino, M., "The Etruscans". London, 1956.
Plowden, Francis, "An Historical Review of the State of Ireland". 2
vol. London, 1803.
Powell, T. G. E., "The Celts". London, 1959.
Prescott, William H., "History of the Conquest of Peru". 2 vol.
Philadelphia, 1880.
Rahner, Hugo, "Greek Myths and Christian Mystery". London, 1963.
Rice, T. Talbot, "The Scythians". London, 1959.
Ripley, William Z., "The Races of Europe". London, 1900.
Ritson, Joseph, "Annals of the Caledonians, Picts, and Scots". 2 vol.
Edinburgh, 1828.
Rivet, Paul, "Maya Cities". London, 1954.
Robertson, John, "The Saxon and the Celt". London, 1897.
Sankalla, H. D,, "Indian Archaeology Today. New York, 1962.
Schliemann, Dr. Henry, Tiryns "The Prehistoric Palace of the Kings of
Tiryns". London, 1886.
Skene, William F., "John of Fordun's Chronicle of the Scottish Nation".
Edinburgh, 1872.
Smith, Dr. William and Prof. Wace, Editors, "Dictionary of Christian
Biography Literature, Sects and Doctrines". Boston, 1877.
Stenberger, Marten, "Sweden". London.
Steward, Julian H., Editor, "Handbook of South American Indians. 6 vol.
Washington, 1946.
Stillingfleet, Edward, "Antiquities of the British Churches". London,
1830
Story, Robert H., "The Apostolic Minist in the Scottish Church".
Edinburgh, 1847.
Thompson, J. Eric S., "Maya Heiroglyphic Writing". Oklahoma, 1962.
Trevelyan, George Macaulay," History of England". London, 1926.
Turner, Sharon, "The History of the Anglo-Saxons". London, 1807.
Vaillant, George C., "Aztecs of Mexico". New York, 1962.
Verrill, A. Hyatt and Ruth Verrill, "America's Ancient Civilizations".
New York, 1953.
Villani, Giovanni, "Cronica". Vol. 1. Florence, 1823.
Waddell, L. A., "The British Edda". London, 1930.
Wade-Evans, A. W., "Nennius' History of the Britons". London, 1938.
Wallace-Hadrill, J. M., "The Long-Haired Kings". London, 1962.
