Tiny O-rings = Airbrush Nozzles

To me those are critical parts/fit and I buy the mfgs part.  Some hobby shops carry the ones for the more popular brands. I find Badger has easy ordering on its web site and good service.

The nozzle for the Neo for Iwata has an o-ring. I don't know about Big Chudy's AB though.

as far as i know you do not use o rings with the nozzle. none of my airbrushes do (iwata hpc plus, doesnt. my badger is a push fit. my cheap 'n cheerful one doesnt either.

of course your could be different. but....i cant find anything on yours to confirm it.

there are o rings further back in the airbrush, but these are to seal the needle not the nozzle.

I don't know of a commercial source but you can make your own. Find a piece of silicon insulated wire of correct diameter and strip a section then cut the insulation into washers. Just a thought.