I seriously doubt you will find any games you want at the airport. Even close to the airport would be difficult, as Schönefeld (city outskirts) is not really a hot spot for gaming. Also, any carry-on luggage has a size limit, but no weight limit (as far as I know), and your check-in luggage always has the same weight limit (23kg if I'm not mistaking), no matter if some items are duty free or not.
I'm going to Berlin for a short holiday, and since I'll bring with me only a small luggage, I'd like to know if there's a game shop into the Schonefeld Airport...so that I could buy something exceeding the weight limit of my cabin luggage :-)
(duty-free items bought inside the airport should not count for the weight limit, is it right?)