Email Scott, Syoung@mseriesbmw.com
Tell him you were told he may have an MZ3 rear axle he would sell. I bought mine off of him, amazing condition (65k) and very honest guy. Packed the living shit out of things, I was amazed. The boxes could have been air-dropped and everything would be intact.
Just be prepared to pay, don't count on less than a grand - and that's a great deal. There are only a few thousand of these cars on the continent and you're looking for a complete rear axle, meaning a car that was crashed without damaging the rear end and not partially cannibalized.