I'd suggest you keep going and go to East or West Glacier or Whitefish. If it were me, I'd go to Whitefish, rent a car, and hit the various Flathead drainages. Nice campgrounds in the park or plenty of private campgrounds on the outskirts.

While Glacier isn't a "noted" Montana fly fishing destination, I just love going up that way every year. It's been my favorite trip the past few summes. The area is just so darn beautiful.