For the ultimate look for a pre '89 go to
http://www.cmwracing.com/ . Unfortunately, the prices will make you weep but where else can you get 17" Fuchs
For a good alternative, try
http://www.cargraphic.de/18zoll.html . Excellent pics and a good resource for checking offsets and what fits in the chart on this link
http://www.cargraphic.de/AnwendungslistePorsche.html