Dax at Laramie GM fills canisters for a couple bucks. At least he did last year. Call and ask for him. Otherwise, if you're riding from the west side, Owenb2 on here said he'll refill for $2 per canister. There was a thread last Jan-March in the Wyoming section.
Last winter we needed one refilled. Dex at GM was not working and no one else would fill it. We tried a couple of other places but no one would fill it due to liability issues. We finally went to one of the snowmobile dealerships and they let us buy a full tank from one of their packs they had. They said they would order another tank for theirs so that was really nice of them.
Somewhere around 350 pumps. Take a few breaks to let stuff cool down. The convenience is worth it to me. I can test fire whenever I want and not worry about store hours somewhere.