how do you get the thunderstone on pokemon fire red?

Question

(for Game boy advance)

Answer 1

when you get to the cross roads, where the guards don't let you pass to the center town, the town on the left/west is celadon - there is a department store that sells thunderstones there, among water, leaf, and firestones

as well, in the powerplant, in the far northwest corner (upper right) there is a thunderstone

Answer 2

go to the dept store at celedon city and buy one