train it
A red gyarados is just a shiny gyarados, it will still take time to accomplish.
they dont have a red gyrados
You can catch red Gyarados anywhere because red Gyarados are only shiny but are extremely rare.
there is no red GYARADOS that you can catch, dont make assumptions. the only way to get a shiny red gyarados is to find a random one and hope that the 1/8192 chance happens
defeat red gyarados.
khadels backyard
To get a red Gyarados in Pokemon LeafGreen you first need to catch a shiny Magikarp. This shiny Magikarp will be able to evolve into a red Gyarados. This is due to the red Gyarados simply being the shiny color of Gyarados.
In Pokemon Crystal version, you catch it at the Lake of Rage.
You cant catch red gyrados in pearl at a pond like you can in Pokemon GSC. It is completely up to chance to catch one while fishing, Its extremely rare. You can use an action replay to hack one but I wouldn't.
Catch a shiny magikarp and evolve it.
GYARADOS
you can't you have to use a cheat or trad it from hg/ss