2003 mountain Aire air ride dump valve location

Based on my experience with my Dutch Star on a Spartan chassis I would suspect the ride height valves berore the dump valve.

Those are the ones that there are three of. Two front and one rear. I haven't replaced one for a few years now, but did replace several and found them at a heavy truck parts supply house. Price then was about $50 +/- and they were a pretty easy job to replace.