I see that Walmart is now selling a Coleman cannister type stove with the same threaded fuel tank attachment as the MSR "pocket rocket" stove, and they carry the fuel replacements. In the past an MSR butane stove user would need to find an REI or EMS type of specialty outdoor store to re-supply fuel. This made the MSR pretty useless for an extended trip in a rural area. With Walmart carrying the MSR size tanks, that stove is now somewhat more practical. There's not a Walmart around every corner in the US, but certainly lots more of them than REI or EMS. Hopefully other hardware chains will carry them in their camp fuel section.http://www.walmart.com/ip/Coleman-Butane-Propane-Mix-Fuel/20595064
I think you could make it coast to coast on the TransAm using the MSR "pocket rocket"or equivalent if you prefer a cannister stove. I've made the trip several times in the past using white gas fuel.
Just for the heck of it I used the "check store availability" tool on the above Walmart link. (It's a boring March day here in NH!). I entered a couple of towns from each state where I remember Walmarts close to the route. "In stock" locations included Williamsburg VA, Christiansburg VA, Hazard, KY, Berea, KY, Carbondale IL, Farmington, MO, Chanute KS, Pittsburg KA, Pueblo CO, and Frisco CO.
You'll run out of Walmarts across WY but there are backpacking stores in Lander WY and W Yellowstone MT. West from there you can fuel up in Missoula MT, Redmond OR and Eugene OR. "Out of stock" today includes Charlottesville VA, Newton KA and Baker City OR, but there are Walmarts and/or backpacking stores in those towns.
A 220g cannister is $4.88 at Walmart, maybe a buck more for the MSR tank at a backpacking store. I would always have a cannister in reserve in case you come to a town out of stock. Yes, $4.88 would buy over a gallon of petrol...... but butane is so convenient.