The GameStop Car was only made available to those who downloaded the car to their Xbox 360 MU from a Xbox 360 Kiosk at a GameStop store. The vehicle itself is simply a re-skin of the Limited R205 GT.
How to UnlockEdit
Download the GameStop Car from an Xbox 360 kiosk at a GameStop Store and then win a medal at the Central Route Traffic Attack Short Reverse in a Rank 9
, which is the same unlock condition as the Limited R205 GT.