You can buy one at the department Store in Celadon City.
The TM thunder is found in the power plant.
You can find the thunder stone in New Mauville
you can find a thunder stone by checking the UNDERGROUND
You can find it anywhere.
They can be brought at the Celadon Department Store.
you find them in mt.moon
me dont nkow
there isn't one there...
You first need a yellow shard these can be found using Dive near the Hunter's house, Second give the yellow shard to the hunter he will trade you a thunder stone for the shard. Another way to get a thunder stone is by trading a Pokemon from firered or leafgreen that is holding one to ruby, sapphire or emerald.
You find the thunder stone in Celadon Mall level 4, wise man gifts.
You can get 2.
Use a thunder stone on an eevee