An Airstream Dealer may have one, but you will have a better chance at a Chevy dealer if need be. The chassis is a Chevy and the engine and chassis systems are all going to be fed off the main block. Sounds like a blow fuseable link to me.
I have no clue where to look for it, so starting with the fuses is a good start. Pull them and check them. If you can't find it there, there may be a failed breaker. Quite often they are under the hood. I would reccomend a voltmeter to check them.
In the newer Electronic transmissions many of the controls require 12 volt
input. The trans may shift from first to second without it, but not go any further without the 12 volts. This is normally a limp mode so you can crawl to a service location.