Cover for third brake light - 92 LS 3dr

I got the third brake light on my wife's '92 LS hatchback working only to find that I seem to be missing a cover for the front portion of it. Without the cover, the brake light reflects off of the rear view mirror and causes a real distraction at night. Have a makeshift cover of duct tape on it now, but anyone know if only the cover itself, and attaching nut/bolt is available online somewhere? Thanks. Jim