Get FREE Marvel Avengers socks when you buy two boxes of specially marked Post cereal! After you get your 2 PIN codes (1 code per box). Locate the unique PIN code found inside specially-marked boxes of Post cereals: Shreddies, Honey Shreddies, Honeycomb, Alpha-Bits, Honey Bunches of Oats – Almond, and Honey Bunches of Oats – Honey Roasted. Two PIN codes required to redeem for one pair of socks. Offer available while supplies last. Offer must be redeemed by May 31, 2019, 11:59 pm ET.