you could catch him in the sea but you have 1 in a million so i would find a shiny magikarp then get him to evolve.
Get surf then go to the sea of rage and swim to the middle of the lake and battle it.And TRY to catch it
simple battle
Actually there is no red Gyrados. I mean there is, but a red Gyrados is a shiny Gyrados.
to get a red gyrados you have 1% of finding a red gyrados and you have to use a super rod to find a red gyrados.
red gyrados is just shiney gyrados use the shiney code and find gyrados
you have to battle the red gyrados then get to team rocket's base and get through it then you can battle in the Mahogany gym the get to pryce
battle the red gyrados at the lake of rage and then go to the souvenir shop
The Red Gyrados drops it. If you already fought the Red Gyrados, you should already find it.
Gyrados's shiny color is red to get a red gyrados is very hard it takes 8000 chances or so to see it keep finding gyrados until its red.
you get a lvl 100 magicarp at the resort area, not a red gyrados
The red Gyrados is found in the Sendoff lake at the Spring Path.
The Red Gyrados is basically a free Shiny one. So you can get another one ether through luck or the Battle Wild Shiny Pokemon Action Replay code