Where do you get a thunder stone in diamond?

You can't get a Thunder Stone in Pokémon Diamond. It's a Generation IV exclusive item, meaning it only appears in Pokémon Pearl and Platinum.

Here are some ways to get a Thunder Stone in those games:

* Route 210: You can find a Thunder Stone on the ground in the tall grass.

* Grand Underground: You can find a Thunder Stone as a hidden item in the Grand Underground.

* Trading: You can trade with another player who has a Thunder Stone.

If you're playing Pokémon Diamond, you'll need to trade with someone who has a Thunder Stone from Pearl or Platinum to obtain one.