Where to get the pokeflute in pokemon heartgold?

You can't get a Pokeflute in Pokemon HeartGold.

The Pokeflute was an item in the original Gold and Silver games that was used to awaken Snorlax. However, in HeartGold and SoulSilver, Snorlax is awakened by interacting with him, and the Pokeflute was removed from the game.