Celadon city.
in the begging of the game theres a gym near pallet town that's where Giovanni is the last gym leader
The fifth Gym Leader in Pokemon LeafGreen is Koga, the leader of Fuschia City's Gym. He specializes in Poison-type Pokemon and hands out the Soul Badge.
The 8th gym leader is in Viridian City.
Go to Pallet Town and Surf down, and you will get to Cinnibar Island. You need to get the secret key from the pokemon mansion on Cinnibar Island to get into the gym.
Step on the portals until you get to the gym leader.
Viridian City, Giovanni(Team Rocket Leader) is the Gym leader.
you fly 2 pallet town and surf south then u have to get through the Pokemon mansion
beat the gym leader
In Fuchisa city
Her name is Erika
On cinnibar island.
you get it at safron city gym leader