When you can surf, go to mauville and make sure you have a basement key, surf to the cave, go in and unlock the door... You go in the water on route 110 right under the sign for the bike road building.
From Mauville City, go south, you'll meet the Fisherman. Surf and keep to east. Then, you reach the New Mauville.
magnetons cannot be found in the wild, however you can find a magnemite in new mauville just outside of mauville
To the leaftnof Mauville
Go south until you are below and out of Mauville City, and Surf in the water until you find a cave: That;s New Mauville.
In mauville city
it is on mauville city
In Mauville City
IN MAUVILLE CITY
Go north of Mauville.
You get the third badge in sapphire when you get to Mauville. You have to battle Gym Leader Wattson in the Mauville City Gym.
At new mauville after you beat your dad go to wattson and he'll give you directions
North of Mauville City