You have to evole from Dratini and Dragonair. I don't know of a way to catch him in the wild.
the way you can catch is go to the safari zone and use the super rod in the water.
dragonite is the strongest dragon there is in leafgreen
Dragonair evolves into Dragonite at level 55.
Dragonite is the last evolution of Dratini.
hyper beam
It can't learn that move cause it doesn't exist in leafgreen.
dragonair evolves at lv 55 but dragonite doesnt evolve
Venusaur,Rapidash,Gyarados,Pikachu,Pidgeot and Dragonite
dragonite doesnt evolve
Go to http://bulbapedia.bulbagarden.net/wiki/Dragonite_(Pokémon) It has a list of all the moves Dragonite can learn in every generation.
Either get a Dratini from FireRed or LeafGreen and train it to level 55 or get the purified one from Pokemon XD: Gale of Darkness.
No if you want one you will need to trade a dratini from firered or leafgreen to sapphire then train it to level 55 OR purify the shadow dragonite in Pokemon xd gale of darkness then trade it to sapphire.
train all your Pokemon at least to level 50. I had a level 58 dragonite so try getting a dratini to evolve.