If you have a *** blick art store near you, go there with your airbrush and see if an iwata or generic cup will thread in. Most airbrushes use standard sizes and many cups will work.
Also tcp global makes generic size cups for $5. Order one of those and try it if the iwata one's don't work. You can also go to your local hardware store and in the plumbing section are brass fittings in all sizes and shapes. See if you can find an elbow shape that will thread in. Then all you have to do is get creative on making a seal for the threads like Teflon tape or petrolium jelly or an oring.
If you find a brass fitting that works, now you know the thread pitch and you can go back to tcp global or the like and see if you can find the right cup. Also Chicago airbrush may be able to help. Email them.
Grex also makes general thread size cups. See if these are at a local retailer, try one of their cups or go to your local ipms chapter meeting and ask the fellow members if any of them have cups you can try and see if they fit.
If you think outside the box and get creative and I am sure you will be able to make something work instead of buying another setup. It's simply a threaded hole.