Welcome to the Forum. I'm not far from you in Gallatin Gateway but am not aware of any modelers in the Butte area. I do get to Butte from time to time. Was there last week and had a great lunch at the Metals.
I'm also not aware of any people into G scale. I have seen many outstanding outdoor G scale layouts on YouTube. I would love to have an outdoor G scale myself but never build it.
I belong the the Livingston Model Railroad Club in Livingston, which is HO scale. In April, we usually have a train show at the old Northern Pacific Depot, which is now a museum, and the following day there is usually a show up in Helena, You might consider checking these shows out and you might meet someone there.