Paul,

I went through the same problem with finding the latest Porsche Winter recommendations for the 996TT. TireRack did not have the latest recommended Pirelli SnowSport 240 N3 tires. My local Porsche dealer was clueless on what the recommendations were or on availability. I had heard excellent things about Wheel Enhancements. http://wheelenhancement.com/
So I gave them a call and spoke to Dave. He was very knowledgeable of the recommendations and had the tires in stock. They obtain their wheels from Porsche. It's worth the call.

Pete