Without having seen it, I'd guess your van started out with factory leaf spring and shocks. The ambulance upfitter likely removed all of that in favor of the much better riding air system. After 20 repairs, you could put a fork in me too, I'd be DONE. Over it.
It's pretty easy to locate an E450 box van ay a wrecking yard, I'd consider comparing what you have currently, see what brackets have been cut off the frame, or maybe they just unbolted stuff, and access the feasability of just converting it back yourself. I'll warn you through, it's 3lb sledge, floor jack and pry bar, steel toed boots wearin', finger pinchin' heavy work. Certainly not difficult, but...
Before you do, take a bunch of pics of the air ride system, you might find that someone else, tired of their factory leaf suspension, would buy it from you.
1995 E350 7.3 Diesel, 4x4 high roof camper, UJOR 4" lift