I have been fairly successful in acquiring interior parts for my '83 M-B either through the recyclers or the dealer.
For recycling, I have used Atlanta-Stuttgart, Aurora Auto Wrecking, and Potomoac German Auto.
In three words, my advice on getting interior parts for older M-B is: Do it fast
These seem to be among the first things that M-B stops making and then become hard to find. One example: I need a right side visor and I've been looking for over a year - still no success.