You can easily capture Gyarados simply by fishing using the Super Rod in certain areas. The area I tend to find them the most in is at Fuchsia City's small pool right above the Warden's Home. To reach the pool enter the house next to the Warden's home and go to the entrance in the back. This will lead you to the small pool now all you need to do is keep using the Super Rod until Gyarados appears.
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.
Red gyarados is actually a shiny pokemon so you would have to catch a shiny magicarp and evolve it in a shiny gyarados (meaning a Red gyarados)
Gyarados
No
You can not catch it in leafgreen,but in firered you can.
... you cant that was just in the show
You can catch red Gyarados anywhere because red Gyarados are only shiny but are extremely rare.
Blastoise is the best but gyarados and cloyster are also very strong
train it
Nowhere no hoenn Pokemon can be captured in leafgreen.
Catch 'em all
"How do I get an ekans in Pokemon leafgreen?"You can't catch an ekans in Pokemon leafgreen, but you can catch it in Pokemon firered and trade it.I got my Ekans at route 10 at lv. 4