Hey Gano, these Americans don't have propane powered vehicles like us Canadians.
There is a propane fill station at the new gas station in Cedarville - http://surprisevalley.us/rabbittraxx.html
I'm not 100% sure they had propane, but i'm about 98% sure. I seem to remember seeing it when filling up last year.
Also there are on playa propane refueling trucks, they service art installs and flame effects on vehicles. Ask Dave X, from BMorg about connecting with these refueling services.
Hope your Bus project turns out awesome!