Participating GameStop stores in the United States and EB Games stores in Canada will start giving out Mega Charizard EX special codes printed on receipts of those that purchase three Pokémon TCG booster packs. The code unlocks one of two Mega Charizard EX cards for the Pokémon TCG Online. Codes will be given out until June 8th, 2014 and players must redeem the code by June 30th, 2014.


Source: http://www.pokemon.com/us/pokemon-news/get-a-bonus-digital-mega-charizard-ex/