I don't post eBay ads much but this one might interest some:
http://m.ebay.com/itm/75-76-77-78-BMW-530I-MANUAL-TRANSMISSION-7764911-/331735962326
http://m.ebay.com/itm/75-76-77-78-BMW-530I-MANUAL-TRANSMISSION-7764911-/331735962326
Why do think this would be a 5 speed?