I made a 911 (996) GT3 in a seperate garage, and then tried to buy it off of the second memory card, but it said "This car is not for sale" I was just wondering why that is? I ended up having to just put the GT3 body onto the RGT.
The Porsche isn't really part of the original game as it was "taken out" so I guess they didn't add that in to save some space. Just make it in your normal garage. If your using MKS, just change the car to the 911...