Missoula, and the surrounding area, is blessed with great water and great flyshops, like the ones already mentioned. I'd also check out Kingfisher, always enjoyed dealing with them; lots of options and they'll steer your friends in the right direction. Rock Creek's a great dry fly stream and gets a nice run of browns moving up out of the Clark Fork in the fall intent on making baby brown trout; getting them to bite on top may be another matter, but the locals are often willing. Just my $.02 here, but I've found it to be a real b.tch to wade, having taken a few dips (one leading to reconstructive knee surgery) even with cleats & studs and I always move a lot more carefully there. Also, the Rock Creek road is no place for cars with low clearance anywhere above MM 10 (or is it 11?). Although he's spent a good portion of the year on the other side of Lolo Pass this year, John should chime in here too; he's got the local perspective.

Regards,
Scott