Right now there is a coupn inside the October issue of Gameinformer that has the B2G1F offer. There is no way to tell how often this sale happens since it has been completely random over the last year.

Probably worth it to buy the magazine just for that coupon. Now just need to find one.

Game Informer is, I believe, only available at GameStop. Your local store should have hundreds of copies. Cover price in the U.S. is $5.99 plus tax.