I'm trying to get past a Snorlax and I need a Poké Flute to wake him up—how do I get one?
First you have to obtain the Silph Scope from the Rocket Hideout in Saffron City.
Then you must travel to the Lavender town Pokemon tower and scale your way to the top.
After defeating Marowak you will have to fight through a few Rocket Grunts, and then Mr. Fuji will give you the Pokeflute as thanks.
You will need the Silph Scope first. Go to the Team Rocket hideout (Celadon City) and best the Team Rocket leader. Then go to Lavender City, into the tower and make your way to the top. Beat a few grunts then Mr Fugi will give you the Pokeflute as thanks.
Then you can go to the Snorlax and battle him.