Protar did a 512S which comes up on ebay every now and again. I haven't started mine yet but it looks quite nicely detailed.
Testors also did one, (could it be the same kit?) and there is one on ebay right now
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=2583&item=5984343726&rd=1&ssPageName=WDVW
Good luck
Martin
http://www.freewebs.com/martsmodels/