EDIT2: The DLC keys have actually been used, they just weren't marked correctly on my spreadsheet.

I found three DLC keys for this game, will send them to the winner via Steam.

DiRT Rally 2.0 - H2 RWD Double Pack DLC
DiRT Rally 2.0 - Opel Manta 400 DLC
DiRT Rally 2.0 - Porsche 911 RGT Rally Spec DLC