Fire Fang is a move that is exclusive to certain Fire-type Pokémon, such as Charizard and Houndoom, and not part of Charmander's movepool.
If you're looking for a Fire-type move for Charmander in the Mystery Dungeon games, he learns:
* Ember at Level 5
* Flamethrower at Level 23
* Fire Blast at Level 41 (depending on the game and version)
Let me know if you have any other questions about Pokémon Mystery Dungeon!