good luck
do you have a re store in your area that might have an old donor fixture ?
I seem to remember reading that Simkar lighting was having financial difficulties if so that is why you’re not hearing back from them, might be cheaper and simpler to replace it with something more efficient. If you have to have a troffer style, LED models have come down in price. Edit: Simkar lighting has probably gone the same route as Smoot-Holman lighting and they ain’t no more.
In a pinch, you should be able to fold light gauge sheet metal over an edge enough to approximate that cover. It might not meet a code but if not inspected with a lot of scrutiny it should suffice. You can get enameled sheet at many stores but better to try and find salvage as the piece might be more expensive than the fixture.
I'm not familiar with that fixture.
I seem to remember reading that Simkar lighting was having financial difficulties if so that is why youÂ’re not hearing back from them, might be cheaper and simpler to replace it with something more efficient.