you must frist go to seafoam island where blaine is, he is the 15th gym leader, then go to cinnibar island and a character who is behind the Pokemon center will then say that he is the last gym leader, once you have talked to him he will go to viridian city gym, he is the last gym leader.
this is for heartgold and soulsilver :)
hope this helped.
Blue, the last gym leader in kanto region
In the first city
blue in viridian city
After you beat the other 7 kanto leaders you will find Blue in the rubble of Cinnebar Island. Talk to him and he will return to Viridian Gym, then you can go battle him.
you have to use surf through passage ways
you can take on any gym leader in kanto in any order (excluding blue you have to battle him last)
the last gym leader is Blue.When you go to the seventh gym leader Blaine you should see Blue and asks you if you have 7 badges then you beat Blaine and go to Blue and he says to meet him at his gym
You need to have defeat the other gym leaders of Kanto first, after that you will find Blue on Cinnabar Island, talk to him and he will return to his gym.
It is Giovanni, the team rocket leader. He's in the Viridian City Gym. Its rumored he murdered the previous gym leader, Blue.
The Kanto gym leaders come in no particular order, but Blaine is typically the last gym leader fought, and also the second to last gym leader appearing on the Trainer Card.
Because Misty is not at her gym, you have to find her up at Route 25.
a city