Air systems are easy to work on, but I would start by finding a Tractor Trailer Truck and Supply shop near you. Our buses share a lot of parts with those vehicles, particularly the air brake system. In the past, I've literally walked into my local shop ATTP (All Truck and Trailer Parts) with a part in my hand that I had no idea about what it did or was called. I showed it to the guy, told him it was leaking air and he said "hold on". 2 minutes later, I had the new pressure relief valve in my hands. Awesome.
Patina enthusiast and professional busman