You might consider coming down further East, just into Alberta, and playing the Stanley Thomson courses in Banff and Jasper.
As for Montana, there are some pleasant courses in the Flathead, Whitefish area. No great shakes architecturally, but in beautiful settings and a pleasant way to spend the day. The old 18 at Whitefish, in particular. Others are Buffalo Hill (Kalispel), and Meadow Lake (Columbia Falls,) Eagle Bend (Big Fork,) and the old nine in Polson. Also, there may be a few newer courses on area Indian Reservations. Again, nothing at all inspiring architecturally, but if you happen to come down through Waterton and Glacier Parks, they might be worth a play.
Missoula has a newer course called either Phantom Links, I think. Part of a development/club called the Ranch Club, but they accept outside play. I've heard mixed things, but haven't played it.
East Missoula has a newer Curley-Schmidt design called Canyon River. I played the back nine. Was not my cup of tea, did not feel like Montana and I found it contrived. But it made the Golf Digest list of good, inexpensive courses for last year, so you may want to check it out. My guess is that many here would like it. Right next to the freeway.
Old Works in Anaconda is definitely worth playing if passing by. Some good, fun holes, some not so good. But interesting because of the setting and the engineering that went into the project. If you are up for an adventure check out the Anaconda Country Club, 9 holes built in 1908. Or the Butte Country Club, 1909, by Alex Findlay. I think the ACC is on the original site, but not sure about the BCC. Anaconda gladly accepts outside play. Not sure about Butte.
Bozeman has some newer courses in the area, but don't know much about them.
Good Luck and Have Fun.