I am not an expert, by any means, nor do I know of any published systematic studies of American Indian powder horns. However, I can tell you there are a lot of horns with native provenance in private and public collections. If you want to look at a variety of them, good places to start would be some of the museum collections databases online. No two of these databases have identical formats, so you may have to fiddle with them a bit and experiment with different search terms to find what you're looking for.
The American Museum of Natural History has a very user-friendly format, and may be a good place to start. Try this link:
AMNH Anthropology Collections Fill in the appropriate spaces in the box on the left side of the screen, click "Search,"... and wait. This site is slow! However, they have a bunch of horns. This is a nice one collected from the Malecite people:
Another is the National Museum of Natural History (Smithsonian):
NMNH Database Keyword SearchAgain, type in your search term and start the search. You'll get a listing of individual items, which may require some sifting to get what you want, but it may be worth it. This horn from the NMNH came from the Comanche, and it is a beauty:
There are others, and I keep finding more all the time. I would suggest you do Google searches. Type in the museum of choice (e.g. Burke Museum or McCord Museum) and add "collections database" and Google should take you where you need to go.
Good luck! If you find something interesting, or see some kind of pattern developing, by all means let us know.
Best regards,
Notchy Bob