You have to trade with another game (either black or white) until you have all three. It's time consuming since the second gameholder has to start over and play the game until the first gym leader is beaten and the c-gear is obtained from Professor Juniper's friend.
I know from experience. It took an entire day, about 20 hours of nonstop playing and restarting, but I had three other people playing with me that wanted all three starters, too.
Or, you could catch a ditto, borrow your friends starter through trade ^, get an egg in the daycare, then give it back to them.
You start your game and get 1 starter then trade it. Then start the game again and pick a different starter. Do the same until you get all of the starters from Pokemon black and white.
To obtain all three starters you need to trade with someone.
the three starters are Tepig, the fire type, Oshowat, the water type, and Snivy, the grass type.
Well, all three of the starters are based on animals.The grass starter is based on a snake.The fire starter is based on a pig.The water starter is based on an otter.Hope this helped.
Trading.
in my heart
It is not possible to get all three starters in Pokemon LeafGreen without trading. This was an intended mechanic to encourage interaction between players.
It is impossible unless you hack
3314775
You can get croconaw, bayleef and quilava.
no because you can die
Mudkip Torchick Treeko (hope this helps)