Nowhere as far as I know. It's all kind of melded into the simracing community as a whole. The standard GPL installation these days seems to have the GPLEA carset in it. Some tracks have been converted into modern platforms and updated to modern standards in the process, e.g. Crystal Palace and Goodwood, and even the car models get rehashed (there's a "Legends" mod in rFactor 2 that was made from the GPLEA models, low-poly though they are).
The biggest shame is that the hilarious page detailing the history of the Pantsring is no longer online...