What Scott said is Gospel.
When you're looking for an air source almost anything will work. I say 'almost' because it does matter how many PSI it can deliver, and whether you can regulate the volume. So you can have a CO2 tank, an refrigerator compressor, or a can of compreesed air and each could conceivably do an excellent job for whatever brush you choose.
Whatever source you pick should have a regulator and a moisture filter. Othre than that, price, noise level, and other bells and whistles come into play.
For the record, I have a couple of Iwata brushes and an Iwata SmartJet compressor, but, as mentioned by Scott, I can use a different compressor if I have the appropriate fittings for the air hose, and my compressor can operate any brand of brush.
Good luck in your search. Check out dixieart.com for excellent prices.
DWR