To get snorlax you need to travel to kanto which you could access after beating the elite 4 and champion. Then you have to have the Pokeflute in your pokegear which requires the EXPN Card which you can get at lavender town in the radio tower. After that you have to play the pokeflute near snorlax and talk with snorlax and it will wake up. Snorlax is found in Route 11 ONLY.
Source : Bulbapedia
