Trade with other people who have heart gold or soul silver.
By cheating or trading with other people.
It is not possible to get all three starters in Pokemon LeafGreen without trading. This was an intended mechanic to encourage interaction between players.
You don't not unless you trade or cheat
By trading the other starters with other players of Diamond or Pearl.
To obtain all three starters you need to trade with someone.
in my heart
Get a friend to trade them to you.
Trade with other people who have heart gold or soul silver.
By cheating or trading with other people.
Train them!
the starters the three dogs ho-oh lugia celebi that's all i can think of
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.
The only way to get all three starters is by trading them. You can do so with the GTS in Goldenrod, or With friends if they have the game. And then there is Action Replay if you want to use cheat codes.
It is not possible to get all three starters in Pokemon LeafGreen without trading. This was an intended mechanic to encourage interaction between players.
Starters are intended to be rare, one-of-a-kind Pokemon. That's not to say there hasn't been a main series Pokemon game that has allowed you to get all of the starters, though - in Pokemon Yellow, you could get all three starters available at the time.
The Availible Starters Are -Chikorita Grass Type Pokemon -Cyndaquill Fire Type Pokemon -Totodile Water Type Pokemon They Are All Availible In Pokemon HeartGold And, Pokemon SoulSilver