Snorlax is a static character and can only be found twice, both times in the Kanto region.

Snorlax appears blocking the path west of Celadon City and entering Router 12 from Vermillion City.

To start the battle with Snorlax you must have the Poke Flute item.

Be sure not to accidentally defeat the Snorlax if you want to catch them, because they do not respawn.