My rebuilt compressor came from these guys
As far as I know the M5 compressor has a different p/n, but these guys had one that fit and it's been working fine for 5 years now. It helped to be in the same city.
I stayed with R12 because I have a life-time supply, but I understand that their compressors may be compatible with R134. You'd have to change all o-rings and perhaps hoses which is a pain.