I think a homemade vacuforming set up would make these relatively easily. Build a box around the part, line it with saran wrap, fill it with plaster of paris to make a cast. There are articles on Pinside and elsewhere about vacuforming that would give details. Then flip the mold over and put a sheet of the appropriate kind of thermoplastic over it. Apply heat (heat gun or ?) and suction (it sits on a sheet of pegboard - you make some kind of manifold box under the pegboard and use a shop vac for suction) and pull the soft plastic down against the mold . Trim it out, cut out the speaker holes with an X-acto, maybe use some kind of leather punch to punch out the light bulb holes.
There are probably some ramp-makers on Pinside that know a lot more about this that could share some info and tell us if it's as easy as I think it is.
I would make a mold like a ring that had a big hole in the middle where the bulbs are. When it's dry, put a piece of pegboard in the hole to allow airflow to suck the plastic sheet down against the mold.