Just want to make sure you actually mean a sponsor and not nay affiliate programmes. If you don't know the difference a sponsor is you supporting a brand / product, typically lending support / review / getting money or services for feedback, promotion etc - whereas an affiate normally comes through the premise of links you get to show different products and you get a slight share of any sales based on the click through for these links.
As mentioned by LW001 Freedom has a wide variety of sponsorship's available on the Freedom dashboard, and allows you copies of games to review in the Game Giveaway section. You may also wish to read Freedom's Best Practise Guide to Sponsorship's which you can view -
HERE