I was poking around the E32 board and saw a reference for Bimmers South. I took a quick look at their prices and they seemed pretty reasonable compared to other prices I've seen on the net. Looks like they parted a 733i and a 735i so they don't have a huge selection of e23 goods:
I've never bought from these guys so I can't attest to their reliability or trustworthiness.
Ted R. '84 745i "Fraulein - looking for a brother....."