Coinco coin doors appear on many ’80s games, including classic Williams video and many Atari titles.
Coinco, also known as Coin Acceptors, is different from Coin Controls, and the doors can be confusingly similar.
Atari used both door styles. Most of the pinball-type doors are Coinco, but by 1983, Atari went to an over-under door and made the same title with both door types.
On the other hand, Williams just used Coinco (I think) or their older door. Defender used the stainless steel door. Williams stuck with that door on the pinball side until around 1985, when games like Comet switched to this door.
Parts for these doors are not generally available. (Coinco the company is still around, but has not provided parts in many years.) I found a few things at Pinball Resource, but I suspect they have little or no stock. Your best bet would be looking for donors. I got some parts from Arcade Boneyard and from asking a local operator who has parted out many of these doors.
There are some minor differences in these doors over their lifetime. The Sinistar door above has a crack in the coin return housing, because it’s plastic. On other doors these were metal and held up to better abuse, but would shed paint.
These doors come apart pretty easily once you take the three 11/32″ stop nuts off the top of the door. The internal steel plate comes off in one piece. This gives access to the coin return buttons.
Or, you can do it the wrong way and try to just take some of the coin mech bracket off. Don’t do this, because it’s easy to crack the plastic lever that keeps the reject button forward in the rest position (this Pinside thread calls it the “porkchop”). These parts are difficult to find.
Some documentation is available here, including parts diagrams.