you have to go to Olivine city and get on the Fast-Ship Pier and you will end up at Vermilion city.
vermillion city
actually there isn't 9 gym leader there is only 8 like the other ones. Actually, the 9th gym leader in heartgold and soulsilver would be the first gym leader in Kanto after you beat the elite four the first time, you can face the kanto gym leaders in any order.
His name is Brock and he is in Pewter City.
In the first city
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.
nothing
The final gym is the Viridian City Gym. Blue is the Gym leader.
Not enough info: which gym leader?
beat the elite four for the first time.
Blaine.
In G/S/C, the 9th gym is the first you battle when you reach Kanto's Vermillion City, the leader Lieutenant Surge.
Blue, the last gym leader in kanto region