Hi Captain. I've just had a look on realoem and the M5 type calipers are fitted to these vehicles:-
E34 540i SEDAN, U.S.
E34 M5 3.6 SEDAN, U.S.
E34 M5 TOURING, Euro
E34 M5 3.6 SEDAN, Euro
E34 M5 3.8 SEDAN, Euro

I looked for the front left caliper as an example, and the part number is 34112226873. I hope this helps you find a suitable donor car.

Cheers,

Shaun M