here you go
Should in theory be the following part numbers for M3
https://parts.bmwnorthwest.com/a/BMW...t/72_0907.html
Front left 72117496293
Front right 72118076367
and
https://parts.bmwnorthwest.com/a/BMW...r/72_0908.html
Rear left 72118076377
Rear center 72118076383
Rear right 72118076378
but i'm also seeing this part number listed for the fronts so
L 72118747229
https://parts.bmwnorthwest.com/p/BMW...118747229.html
R 72118747216
https://parts.bmwnorthwest.com/p/BMW...118747216.html
I think the second links are for the seatbelts with the reverse electromotive belt retractor (REMA) or self-tightening function. At least that is what my Google-fu says.