I actually would think of that as a single unit. I have seen return fittings with lamps in them and if they fail, you replace the whole assembly. I have also seen water powered LEDs. Is the fixture a single piece or is it a collection of fittings plus the lamp body?
Most the the return fittings, non-lighted, are actually made of of several different pieces and they can be bought separately or together. The tailpiece outside the pool would be called a hose adapter.
Do you have a good above ground parts dealer nearby? I have found my AG shop to be very helpful in resolving fitting issues.