You can't reach johto in leafgreen.
you can´t
You're in the Kanto region in LeafGreen and FireRed.
You are currently in the kanto region!
Kanto.
kanto
you are already in the kanto region when you start the games
Electabuzz
Not including Kanto Pokemon their are 235 pokemon in the National Dex. With Kanto Pokemon included their are 386 pokemon in the entire pokedex.
johoto or kanto regions
Johto and Kanto
To get Kanto region Pokemon (Yellow takes place in Kanto), you must migrate Pokemon from the GBA versions of FireRed and LeafGreen.
kanto -- Kanto, with the addition of the Seven Sevii Islands!