Surface mounted lights
We had the same problem with a dual lens fixture in the living area. Switch failed in the “on” position. Our local electronics store wanted $5 for the 3 position switch and a new fixture ordered via Airstream was $9. I robbed an original from the bedroom and installed in the living area so they would all match looking down the center of the AS.
If you replace the entire fixture make sure the new is large enough to cover the footprint of the old. If you can make the old work with a bit of surgery and soldering the connections, there is something to be said for keeping the original light in place.
Search for RV lighting, campingworld.com (dome lights), etc.
Airstream parts dept. measured what was in their inventory so I knew exactly what area would be covered.
Hope this helps.
Travelers by aluminum roadships, loyalists to one species,
masters of convenience, herdsmen steeped in maintenance and restoration.