you go to Stevens house and he gives you dive. then you go to sootopolis city which you have to dive to get to.
To Steven's house in Mossdeep City.
you can get a sun stone from the space center in mossdeep city.
You have to beat the gym leader first... then you'll find them there.
Go to mossdeep city!
To get to Mossdeep City, you have to defeat the other six Gym Leaders, and you need Surf. In Mossdeep, there is a Psychic-type Gym, and Team Magma will be in the Rocket place.
They have ran to a cave nearby the last city
Go to Steven's House.
In Mossdeep City from Steven after you have defeated Team Magma.
battle theyr boss maxy
After Beating Team Magmayou go to Steven's house, which is the house in the top/left corner of mossdeep city. then he gives you DIVE. teach it to a water Pokemon. Then SURF south of mossdeep city until you come to a part of the sea that is dark blue. go over it and DIVE. Go south until you see an underwater cave. Go in it, there should be a submarine in it, and use DIVE again. Go through the cave until you reach kyogre, and then Archie will attack you. beat him, and then go to sootpolis city.
You will get it in mossdeep city from steven after you fight team magma in tha space center.
Fortree City