There is a guy in Hotchkiss, Colorado (westerm part of the state) that is way into it. 1960's western garb, buffalo gun, the horse, glassing with a pocket telescope for free ranging Bison, the whole deal. I guess he prefers you to dress the part to and use a buffalo gun, or at least black powder.
I will post here in a couple of hours when I track down the info.
Also, large herds of free ranging Bison in the Greater Yellowstone country on both the WY and MT sides.
I believe there is free ranging Bison in western ND, around Teddy Roosevelt national monument.
I'll check on the CO guy.