Mentioning Bambi air compressors, you may be able to pick up a failed one, cheap.
DON'T test it with the cover off! If you do, you'll never rust!
The one at church failed. We stripped it out and a 1/4 UNF bolt had failed. It held a sort of welsh washer over a cast chamber, but had broken off flush with the bottom of the chamber. Drilling out was a nightmare. The head was embossed "12.9". At the cost of two drills, (one hard tipped) drilled it out and enlarged the hole so that could be tapped 1/2 x 40 tpi, Made up a stud, tapped 1/4 UNF at the upper end, and Loctited it in. Sealed the welsh washer to the chamber and the bolt with hylomar. As John Stevenson would have said, "Job's a good 'un" Works just like it always did. A replacement would have been £800!
Howard