Where do you get the move fly in Pokemon platnium?

You get the move Fly in Pokémon Platinum at the Pokémon Fan Club in Veilstone City, after defeating the Elite Four.

Here's how to get it:

1. Beat the Elite Four: Once you've defeated the Elite Four and become the Pokémon League Champion, return to Veilstone City.

2. Visit the Pokémon Fan Club: The Fan Club is located near the Contest Spectacular area.

3. Talk to the receptionist: Speak to the receptionist at the front desk. They will reward you with the TM for Fly.

Note: You can only learn the move Fly on Pokémon who know the move "Fly" or "Sky Attack."