If you are referring to Steven Stone, he is not a Gym Leader. In Ruby and Sapphire he's the Champion, and in Emerald you can find him in the upper area of Meteor Falls after championing the Elite Four.
you have to find steven get a Devon scope and use it on the invisible keckleon in front of the gym
sootopolis gym
It's only locked until you have confronted Kyogre inside the Cave of Origion where you have only 1 chance of capturing it. After that, then you can head to the gym once you have talked with Steven who will be in front of the Gym then you can go inside and battle the Gym Leader Wallace the Master of Water.
in emerald the crisis.(where rayquaza kyogre and groudon are.)
You can find Steven near the gym is Sootoplis City. When you find him, he will take you to the cave of origin.
The last gym is in sootopolis, you need to get rayquaza to get in, you get dive in steven's house - talk to him. p.s: In steven's house you will see a pokeball that you can take - in it there is a buldom level five.
Fortee city winona flying gym, but you have to get the Devon scope from steven on route 120
after you beat mossdeep gym talk to steven go to steven's house in moss deep town
After you beat the Gym Leader, Steven gives it to you.
A Devon scope.
lilicove city gym and then steven will com and give you
in cave in dat one place