It is not possible to find any Charizard or its relavites in wild in the Unova Region, in other words, not in your game. Howerver, if you own one of them in HeartGold, SoulSilver, Diamond, Pearl or Plantinum, you can migerate them to your game via PokeTransfer, which you will find on the Route to the left of White Forest/Black City, however unaccsessible before defeating Ghetsis in N's Castle (in other words, completing the main story.)
