I don’t have anything on a sublet, but Montana’s legislative session ends early May, so people will be clearing out of town around then.
As for the community we are small but active. The climbing (bouldering) gym in town is really friendly and a great place to meet climbing partners. The Helena climbers coalition also hosts Tuesday climbs after work in the summer, and there’s usually a good crowd.
I can put up your email on the gym’s cork board with what your looking for if you’d like though.