There may be a reason these are hard to find. I don't think
they're needed - at least my '81 locks fine - has a small
plunger hooked to the door lock vacuum that locks the cover.
When you lock the doors, a pin slides into a small tab with
a hole on the cover piece - did they discontinue this in 82/83?
Or was it an option?

Do you have a small hole in the body opposite the hinge side of
the cover and a tab with a small hole in it on the cover? If so,
maybe you can add the vacuum plunger/pin (and a foot or so of
vacuum line) to yours. Since the vacuum bottle is in the trunk
on these cars, it should be easy to connect to.

Conrad

I don't think you're going to find one since there would be almost no market
for anyone manufacturing such a product. All of these vehicles came with the
vacuum lock on the fuel door. If your door locks work your fuel door lock
should as well. If not you need some work chasing down leaks in the vacuum
system. I bought a repair manual from http://www.mercedessource.com/ and it
was very helpful. I also bought a small hand-operated vacuum pump from Pep
Boys for about $35 to do the complete job. My problem was one of the vacuum
diaphrams which operate the the door locks but found a new one for $22
locally. Good luck!