You can't be a gym leader in any of the pokemon games, you can jusr beat them and earn the badges you need to complete the elite 4
The fourth gym leader in Pokemon Soul Silver is in Ecruteak City.
in his gym
claire
the 16th gym leader is:Trainer Blue
get a Pokemon with a ressisstance
The first Gym Leader who is Falkner, the Violet City Gym Leader, he has a Pidgey and a Pidgeotto.
He is on Cinnabarr Island.
go to the Pokemon gym
The Gym and Gym leader is in the bottom left of the city near the Pokemon center.
Blue, the last gym leader in kanto region
Ghost Pokemon.
You battle the 8th gym leader, Clair, at Blackthorn City.