How do you get a thunder stone in platinum?

You can't get a Thunder Stone in Pokémon Platinum directly. However, you can obtain it indirectly through trading or by using the GTS.

Here are the ways to obtain a Thunder Stone in Platinum:

* Trading: You can trade with other players who have a Thunder Stone. This is probably the easiest way to obtain one.

* GTS (Global Trade System): You can offer a Pokémon you don't need in exchange for a Thunder Stone. You can search for "Thunder Stone" on the GTS and see if anyone has it listed.

* Wi-Fi Connection: You can connect to the internet and trade with other players who have a Thunder Stone.

Note: You can also obtain a Thunder Stone in other Pokémon games and trade it to your Platinum game.

Remember that the Thunder Stone is used to evolve certain Pokémon, such as Pikachu, Eelektrik, and Electivire. So make sure you have the right Pokémon before using it.