you need hm surf.fight aqua's team and beat the rival.follow existing road.
You can only get the Sixth Badge from the Sixth gym leader. After defeating the Sixth gym leader, the gym leader will give you the Sixth Badge.
the sixth gym is in canalave city
In the Kanto region, the sixth gym is in Saffron City. The gym leader is Sabrina.
BEAT THE GYM
The Sixth Gym leader is Chuck, he has a Hiryama and a Poliwrath.
The sixth gym is Winona, the Flying type leader in Fortree City.
The Fortree gym.
the sixth gym leader is in canalave city. hope that helped. :D
The sixth gym AKA the fortree city gym specializes in Flying Type Pokemon.
The sixth gym is Mossdeep City Gym - Gym Leaders Liza and Tate (Mind Badge). You have to surf right of Lilycove city.
Winona, in Fortree City, is the sixth gym leader and uses flying pokémon.
The sixth gym is in Fuschia City, where you fight Koga, Poison type leader.