I have never come across one. It would probably be simpler to make one. That is what I am doing when the car finally gets into working order again.

I attached some pictures of the hitch made for the car. I hope this helps. If you do decide to try and buy one good luck to you!
(None of the pictures are mine I found them and stashed them in my W124 folder)
Dan

Attached Thumbnails

     

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1991 Mercedes 300TE (Current Girlfriend )
1994 Mazda Miata