I know I asked for the locations of thunder stones, but I need to know the locations of leaf stones too.
Johto: National Park (Come 1st in Bug Catching Contest), Route 34 (PokéGear Phonecall) Kanto: Route 25 (Show Bill's Grandfather an Oddish), Viridian Forest
Also in the Pokeathlon Dome on Thursdays and Saturdays for 2,500 Points. Source