Seriously? The car is part of the Brit DLC pack that hasn't been released to retail version yet. Please read: Automobilista - August Development Update
It's part of the Brit Pack DLC so if you have bought the season pass it will move to AMS when the entire pack is released. As far as I know there's no way to manually move stock content as it's embedded in the exe. And if you haven't paid for the DLC it would be illegal anyway.
If you have the beta you have the dlc pass already one way or another. So once the dlc is released...