Where can you find poke-flute in Pokemon Red?

You can't find a Poke Flute in Pokemon Red.

The Poke Flute is a special item introduced in Pokemon Gold and Silver. It's used to wake up Snorlax who is blocking your path in certain areas.

In Pokemon Red, you can find a special item called the S.S. Ticket, which is required to board the S.S. Anne. This is the equivalent of the Poke Flute in Red, as it allows you to encounter Snorlax on the ship.