Bob
There is shop just south of 285 off of Peachtree industrial that did one for me for $45. They said they could easily fab the channels too. There name is Ellison Manufacturing.
Why back doors go missing? Easy .. the locks usually get messed with and the door doesn't stay closed. They then sit behind the pinball machine. Somebody who doesn't know anything about a pinball machine moves it .. finds the door .. wonders what's this and promply throws it away.
Mike V