I have a 1991 HR alumi-lite. Had to fix the exterior running light a few years ago. Having to replace running light is fairly common and most RV makers use very common models. I have a very good RV parts store nearby, so it was just a matter of going there and matching the same size and type of fixture. They stocked the whole fixture or just the lens. SO, find a good RV parts store in your town. BTW, the replacement fixture (if your are replacing the whole unit) does not really have to be the exact same model, just make sure it covers the section of the old unit. They all work on 12 volts. Also, make sure you get the correct color lens , it depends on the location on the coach. If not near an RV store, as mentioned google is your friend. I have also seen a limited supply of running light fixtures in auto parts stores.
Hope this helps,