Howdy,
Herter's SA revolvers were made by J. P. Sauer in Germany. I think they sold them under the name Werstern Marshall or some such. They have the four-click hammer with a captive firing pin like the old Rugers. They appear to be strong, well-made guns and I am currently after one that my buddy inherited. As for the grips, I would bet that SAA or Ruger grips would come awfully close to fitting. Find someone who will let you borrow a grip panel and try it, then order an aftermarket set.
Bitterroot