As my signature indicates, I have a 2000 HR Endeavor with cat engine. On mine, the chassis manufacturer (freightliner) purchased and installed the air brake tredle, accellerator assembly, and the dash instruments. The coach builder (Holiday Rambler/Monaco) sourced and installed the heat/air system, the radio, etc.
If it is built on a freightliner chassis, you can get parts from freightliner.
Fred & Vicki
Richmond Hill, Ga
2000 H.R.Endeavor/Freightliner/330 Cat