How do you get the azure flute in Pokemon black 2 and white 2?

You can't get the Azure Flute in Pokémon Black 2 and White 2. It's a special item from the original Black and White games, used to summon the legendary Pokémon, Cobalion, Terrakion, and Virizion.

These Pokémon are not available in Black 2 and White 2. The only way to obtain these legendary Pokémon in these games is through trading from someone who owns Black and White.

If you're looking to get the legendary Swords of Justice, you'll need to trade with someone who has Black and White.