The Aston Martin P1 and the Mazda Furai
Enduracers "Bonuses" can be found here: http://f1classic.your-talk.com/t4574p210-endurance-series-service-pack-1-finally-released about five posts down with precise instructions..
And if you're looking for even more GT cars with even better physics and ultimate realism check out IMSA GT by rFactor-league.com IMSA GT can be found Here.
I DON'T OWN ANY MODS IN THIS POST; THE SKINS FOR THE R15 ARE MINE.
Here is the link the the Audi skins: http://www.mediafire.com/?n2v73d5ipbjdr7j Works with all of your R15 mods and comes with 4 skins.