Lee,
Not very common on E30's
BBS did make some RC's with the correct BMW offset many years ago, but they are NLA. Your best bet is to search around on the VW forums and eBay.de.
RC's for 4 stud VW Golf's etc are the same bolt pattern and hub size as the E30 version, but they have a 35mm offset instead of around 25mm for an E30. You will need to use a 10mm spacer to correct the offset, but this is not a problem if you use decent quality H&R or Eibach spacers.
Happy hunting.
Cheers,
Ian.
If it aint broke - Modify it...