Is the problem finding the part, or that you don't know what's wrong (you said 2 mechanics can't figure it out). The dash a/c is a pretty standard automtive unit, with the compressor and such supplied as part of the chassis and the dash plumbing, control valves, etc. supplied by the RV builder. Most RV manufacturers used Evans Tempco components for the dash and a HVAC controller from some Ford or GM vehicle.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL