I don't know of a group like that but we'd be on it in a heartbeat if there were. I lived in BZN for quite a while and now reside in CO. Still have lots of close friends in MT.
Have you taken your AS out on trips in MT? If so, where and which spots did you like?
I finished a float on the Stone with a friend of mine and when we put out, there was a guy camping with a truck camper and a honda generator at the putout on the river in Paradise Valley. I noted the location for a future outing as he had the place to himself.
I belong to a women's fly fishing group here in CO and they organize camping/group trips almost every weekend of the spring, summer and fall but it is not limited to Airstreams. It's a lot of fun since the group trips provide a lot of camaraderie and everyone participating loves fishing.