I have an old 2 bay hopper from Athearn. It has shed its coupler draft gear cover, a metal 3 sided affair with a slot on each side. I have tried to cement another plastic cover on but the #148 coupler binds. Where can I get a replacemet cover like the one that came with the car?
Those Athearn coupler box covers are a very common item that most hobby shops that sell Athearn products should have in stock. They come in a paper envelope much like Kadee couplers and you get something like 10 covers per envelope.
Athearns own website shows a parts section. If you can precisely identify the car in question, you can get spare parts.
It’s best to have a hobby shop do the ordering for you once you inform them of the parts that are needed. I usually buy spares for my boxcar fleet this way.