Are you looking for Amiga computer service manuals only, or for peripherals too? I have a collection myself, but only these two I have double:
* Service manual Genlock, released June 1987, part number 314983-01
* Service manual A590, released August, 1989, part number 314899-01
Asking price 15 Euro for the two together.
Other than this, softhut.com still have several different service manuals available.