Forza 4 Unicorn Cars

Forza 4 has 17 unicorn cars. Unicorns are basically cars that are rare in the wild (RL or real life) as well as in-game. You cannot go to the dealership and buy these cars, nor can you gift them or sell them on the auction house. These cars can be quite difficult to come by, but since we now have so many (Forza 3 had a total of 3), hopefully there will be many more community events where they are winnable. Otherwise, you need multiple millions of credits to buy them on the auction house when Turn 10 puts them up for auction.

Here is the list:
2002 BMW M3-GTR "Street Version"
1969 Chevy Camaro SS Coupe
2007 Ferrari 430 Scuderia
2003 Ferrari Challenge Stradale
2007 Shelby GT500
2004 Mugen Civic Type-R
2002 Mugen Integra Type-R
2005 Honda NSX-R GT
2007 Lamborghini Gallardo Superleggera
2007 Lambo Murciélago LP640
2002 Mazda RX-7 Spirit R Type-A
2006 HKS Time Attack Evolution CT230R
1993 MINE'S R32 Skyline GT-R
2002 MINE'S R34 Skyline GT-R
2004 Top Secret Silvia D1-Spec S15
2006 Subaru Impreza S204
2002 Top Secret 0-300 Supra