The sixth gym leader is in the top of the lighthouse. She is caring for the sick Pokemon. You must go to Cianwood City, get the secretpotion, and bring it back to her. Once you do, she will return to her gym. You can battle her at that point.
You can do the gym leaders in any order you want, although from the Fire Red/Leaf Green point of view the 6th gym leader would be either Misty or Erika.
You find Blaine in the islands that are close to Cinnabar.
I think you need to beat 7 kanto gym leaders to fight him.
in saffron city gym and her name is Sabrina
Route 1 in Kanto
a city
You can find him outside the Power Plant in Kanto.
The Viridian Gym leader (Blue) is at Cinnebar Island, you can go there by surfing south from Pallet Town. If you want him to return to his Gym you have to beat the other 7 Gym leaders in Kanto
Ummm... Which Pokemon game?
they leave kanto to find more rarepokemon with the rocket leader (8 gym leader).
in heart gold and soul silver in kanto on route 7
in one of the kanto leader maps lt.surge!!!