Spa Jet Help

We are having our pool and attached spa replastered. The plaster company is having trouble tracking down replacement returns for the spa. Below are photos.

Does anyone know how I would go about replacing the jet or even just the eyeballs and retaining rings?

I would also be open to just having a more standard fitting (not recessed). I tried just screwing in one like this into the existing opening vacated by the retaining ring, but it was very difficult to turn and I was afraid to force it.

Thank you in advance