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.
Train them!
Get a friend to trade them to you.
cheats
Trade with other people who have heart gold or soul silver.
By cheating or trading with other people.
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
the starters the three dogs ho-oh lugia celebi that's all i can think of
no only johto and kanto but you can get the 3 hoenn starters
All those pokemon would need to be migrated to Heartgold/Soulsilver.
1. you can get them in trade. 2. action replay. 3. hacking.
you either have to trade with a friend or use an action replay code to catch another trainers Pokemon.
You can't- unless you trade