With the exception of the drawing hunt for Yellowstone bison (which are essentially tame animals) all bison hunts in Montana are privately owned livestock. The Crow Tribe in southeastern Montana has a rather large herd that roams a large area and is probably the closest thing to a wild herd around that you can pay to hunt. There's really no sport in hunting fenced bison whatsoever and it's really just killing and not hunting. If that's your cup of tea than more power to you, but it's not hunting.