http://www.buffaloarms.com has Vickerman seating dies for about $80. For an additional $50 they will sell you a compression stem that fits the die. They appear to be out of 45/70 dies at this time, but you can get their phone number at their site, and call them.
If you are loading for a single shot rifle,and your cartridges will be only used in one rifle, there is an effective, cheap, and more convenient way to compress your charge to seating depth.
First, you do not size your cases.
After dropping your charge, put a 45 cal card wad in the case, then use your seating die and a hard (straight Linotype or wheel wieght) sized, un-lubed bullet to compress to seating depth. Then remove the hard bullet, and seat a lubed soft one. For range loads, I don't even crimp, but I do raise the seating stem, and put a light crimp on a few for hunting loads.
After learning this from some local long range shooters, I liked it so well, that I went to a swap meet, and traded my compression die for some Goex and bullet metal.
