Snorlax is pretty easy to get once you have what you need. First, after you give the machine part to the Power Plant, make your way towards Lavender Town, and go into the Radio Tower. Once you're inside, go all the way to the right and talk to the man in the broadcast room. He'll upgrade your PokeGear. Go by the Snorlax, go to the PokeGear's radio, and move the dot towards the top. That will be where the PokeFlute song will play. Interact with the Snorlax, and it'll wake up in anger. Then it will challenge you to a battle.