You have to go to mossdeep city and battle the gym leaders, there are 2 of them in a double battle. Your Pokemon should be on level 50 or more before you challenge them though, because they are tough.
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GET THE LAST BADGE......
Head to lavaridge town for your next badge.
the seventh gym badge snowpoint gym
when you get your seventh badge and you will head for mount cornet
Beat the Gym Leader