Beat the 8th gym leader which is Clair in Black Thorn gym obviously in Black Thorn city.
Go through Ice Path on Route 44
go talk to professor elm after you beat the eighth gym leader
You get a master ball after defeating the eighth gym. You'll receive it from prof. Elm.
you have to beat all 7 other gyms in kanto then go to cinnabar island and he will be there. you talk to him and he disapears and he will be at the gym in viridian
in mossdeep city
Saffron city.
Saffron city.
Cinnibar island.
The seventh gym badge in Emerald is located in Mossdeep City.
I think you get it in either cinnabar island gym or virdiran city gym
in the johto region its in blackthorn city and in the kanto region its in virdian cityblackthorn cityBlackthorn City, past the Ice Cave.
Clair and she is the leader of blackthorn city or if you mean the kanto leader its blue/Gary ashes rivle