You might want to try West Yellowstone, MT too. This town is surounded by more flyfishing than any place I've ever lived in. There are 6 flyshops in a town of about 600 folks and seems like about a third of them are guides or have been guides. Think your best chance is to get a job in one of the shops in sales and work your way into a guide job. There are guides that leave at the end of August for other work. Fishing gets real busy in the fall and I think if you prove yourself working in a shop there might be a chance for you to finish out the year guiding. Plus your flyfishing skills should really improve fishing the Henerys fork, the Madison, Hebgan Lake Gulpers and the rivers inside Yellowstone park. There isn't anything like it or difficult here in Washington that I know about.
Good Luck!