I have been told Mr Briney will sail me there, but he is no where to be seen near his shack.I have saved Peeko and have been searching frantically for hours trying to get there.
Thanks in advance, Skymin.
Just walk west from Mauville City. No tricks required. (Mr. Briney sails you to Dewford, by which you then go to Slateport, then to Mauville.)