you can't by catching but to do so you'll need the following
1. gamecube to gameboy link cable
2.gameboy advance or sp
3. a wii or gamecube
start a new game and get a pokedex, your starter, and another pokemon.
send the starter to colosseum or xd gale of darkness and repeat step 1
You don't not unless you trade or cheat
Sorry, but the only way to get all the starters from Pokemon Crystal to Fire Red or to Pokemon Emerald is to get a gameshark and do it from there.
cheats
you get them by catching all 200 Pokemon
Trading.
You can first collect all of the Pokemon for the hoen dex in Pokemon emerald you will get 1 of the 3 Pokemon gold/silver/crystle series starters then use the get all of the starters trick to get them all then migrate them to Pokemon diamond or pearl.
cindaquil must be migrated from emerald version... in emerald, once you catch all the pokemon, the professor offers you one of three pokemon... you may pick from the johto starters (cindaquil, chikorita, and totodile)
You can only get one of the three Starters in Pokémon Emerald without use of cheating or trading. You can trade or use an action replay code to get all three (I don't know the code, so I can't help you there). Hope this helped.
To obtain all three starters you need to trade with someone.
Yes you have to trade because you can't get all the Pokemon alone.
Yes and no. You do need all three starters, and you need every legendary except for Deoxys, Celebi, and Jirachi.
beat the elite four get a gameshark and the code is:qw7av78cvbfhg4.=5544577 788955258858 4785dfvhrbdnqaz7 47852145ssdczskl;