Originally Posted by Sky Girl
Though this is in the wrong board I'll answer your question anyway. It's really hard to find one but they're in Kanto between Viridian and Pewter City. I'll go check the route.
It belongs in the "Game Boy Games: RBY/GSC" board.
EDIT: Pikachu can be found on Route 2 to be exact.
This is the "gamboy games:RBY/GSC board"
Just search for it in the Viridian Forest.That's where I found mine.