I work in Yellowstone Park and there was a photographer A. F. Thrasher who took photos in Yellowstone and parts of Montana in the late 1800's. Yellowstone's archives might be interested in your photos depending on what they show. Do you still have them? Could you describe them or maybe send digital copies? If so, you can email the digital pics to me at email@example.com
(yep i had a little encounter with a mama griz in Yellowstone in 1994).
I hope my request isn't too much trouble. I give talks on Yellowstone history and am friends with Yellowstone Park's archivist and we are always on the lookout for Yellowstone items from the past :-), and would be happy even with digital copies if you weren't willing to part with the originals.
Thanks so much.
PO Box 418
Gardiner MT firstname.lastname@example.org