Burley Idaho ain't bad, if you're good at climbing the cyclone "security" fence (I am, if its for gas) right across the street.
Mountain Home FBO sells Mogas last I heard
Afton Wyoming has a gas station at the end of the old airstrip, now the Aviat strip, although there has been some junk in the way lately, not sure if that's to keep planes out or just handy paved storage!
I used to get gas in Hailey, before they went to a controlled tower, right across the north end of the runway there is a convinence store, the gate was unlocked and I'd push the plane across the highway to the pump. Can't do that now, for sure.
Smiley Creek, maybe ethonal by now.
Three Forks Montana, a 1/2 mile walk though.
I found out about Delle,UT the day after filling up at Cedar City, coming back from last years Copperstate, Cedar City (boo, hiss) was damn near 5 bucks a gallon. Paying top dollar for AV gas really tees off a pilot with an engine that prefers unleaded mogas (Rotax 912), its a double whammy!
I figured I carried a minimum of 1,000 gallons of mo gas using my first Montague folding bike and my first S-7. 5 gallons at a time (two 2 1/2 jugs), I just hung them from the handlebars, simple and worked great. 4 gph at most, makes this doable, that and being cheap, in shape, and landing places with no other options! I still go XC with a couple 2 1/2 jugs (carried empty on a custom rack in the tail cone), still carry the bike (have to get to the bar) but now have less need due to more range and more carried fuel, not to mention the whole ethonal thing. My 12 gallon ferry tank comes out in seconds, so that and the jugs gets me 17 gallons, that only works if I have wheels, as in a borrowed car.