The thunderstone can be found at Sunyshore City. Go to the Vista lighthouse and go down the stairs. At the bottom there will be a thunderstone. You can also dig these up in the underground.
To get a thunder stone, or any type of stone on Pokemon pearl, you need to go underground and look for a bit, I found this the easiest way to get stones.
You can get the thunder stone by going underground and digging for it in Pokemon diamond/pearl ( the thunder stone , fire stone, water stone, and the leaf stone is very rare, so good luck!).
sunyshore city or the underground
give a pikachu a thunder stone
trade it over from diamond/pearl/platinum
On a pikachu to evolve to a raichu
eevee and pikachu
It would be the same as PKMN Pearl & PKMN Platinum. In Diamond, you can get it in The Underground & Route 213. In Platinum, you can find it in the Solaceon Ruins. You must have a Poliwhirl, a Shellder, a Staryu, an Eevee, or a Lombre seeing you want a Water Stone.
underground using explorer kit
you have to evolve eve using a thunder stone to get joltion
nothing if you give him/her a thunder stone it will lvl up
The Thunder Stone can be found in the Underground, Sunyshore City, and the Solaceon Ruins. The Thunder Stone is used to evolve some Pokemon like Pikachu.