It may have been made in-house... or possibly made by Teak Isle as they are a big producer of these things. It's possible that your boat had a simple, vertical piece of canvas to cover the companionway opening. And, maybe the door was an option... or maybe it was something that was introduced in later model years. "Typically", these doors set into a recess in the vertical section of the companionway to avoid being in your way when stowed.
-- Does your boat have a recessed area?
-- Look closely at a newer boat that has that feature and see if it has a recess.
-- If it will work, you can get the door from your Grady dealer... possibly Teak Isle... or either make yourself or have it made for you.
OR... just have a piece of canvas cut to fit and pop some snaps in it.