How do you catch larvitar in Pokemon FireRed?

Answer 1

go to island 6 or 7 i forgot and then one of the islands will have a canyon and then go search in the canyon and you will find a larvitar in the grass. I've tried and now I have a Trianitar.

It's in Seven Island, in the Sevault Canyon at lvl 10, 15 or 20.
South Seven Island (Of the Sevii Islands) in Sevault Canyon
on seven island ... go down the boardwalk and in the grass you might find larvitar it rarely happens though it took me around 45 minutes
Answer

get a rainbow pass this is how to get one, you must go to island 1 and beat two team rocket people. then go into the cave. you will need to know the move strength. careful when you move the boulders. its kinda tricky so look it over before you move them. you will run into two paths, one going down and one the same way you were going. DO NOT go the same way, go down. you will go down a latter and into a room with little boxes with braille on them. don't worry about them. just go down into the latter at the bottom of the room. you will now find the ruby! to get out, use an escape rope or if you don't have one, go to the other path that you didn't go down. keep going into the latters until you see a wall to jump off of. jump off and go right. know go and see celio at the PC and talk to him. take the next favor and he will give you a rainbow pass. MISSION ACCOMPLISHED! Go to island 7 and go to SEVAULT CANYON where you may find a larvitar catch is with a altra ball. If you want then train it to level 30 to get a pupitar and then train the pupitar to level 55 to get your tyranitar