All the stuff from my files on the Midway coin door is over on Michael Roma's website:
http://home.comcast.net/~mtpacifico/_kenskorner/files/Midway Coin Door - Ms Pac Door.pdf
Yes, indeed Happ Controls bought the dies and rights to manufacture the door from Midway. Happ last showed the door (along with Happ part numbers) in their 1994 catalog. If you telephone Happ Controls, I'm sure they can tell you what they have left in stock for these doors if you give them the Happ part numbers. I'm sure if they get enough requests, they can rerun these doors as complete assemblies again since they already have the tooling and original dies & blueprints.
The history of this door starts around 1968 or 1969. It was originally contract manufactured by Coin Mechanisms, Inc. (
http://www.coinmech.com/) for Midway Manufacturing to use on their electromechanical arcade machines. When the video boom started in 1979, some other companies bought the Midway door to use on their own machines. I can confirm that Ramtek used this door on their games.
Happ was the last manufacturer to make this door, so remaining stock of parts would be from them. I'm pretty sure the patents on this door expired long ago even if the patent had been renewed. You should be able to manufacture this door and sell it, just don't use any copyrighted Midway artwork/logos/trademarks on it. Leave it up to the door buyer to finish it off with a Midway logo plate they "find" elsewhere if you know what I mean.