How To Get All Three Johto Starters (No Trading):

1. Start a New Game: Set the time, talk to your mom,
set up your bank, blah blah.
2. Make your way to Prof. Elm but DO NOT pick your Pokemon!
Save your game right in front of Prof. Elm,
don't turn off the power, duh.
3. Now, you can choose a Pokemon (choose wisely...or not)
From this point on DO NOT SAVE THE GAME! Until I say.
4. Make your way through the game until you have pokeballs.
5. Catch any Pokemon (Sentret, HootHoot, Pidgey, etc.)
6. Give your starting Pokemon 1 Pokeball.
7. Go to a Pokemon Center and deposit your starter into
the PC, then change the Box to any other box.
Save the game,
> BUT! <
Turn off the power when instructed not to do so.
(When the 'R' in 'POWER' appears)
8. Turn the power back on, and you should be standing by
Prof. Elm!
9. Choose a new starter (One you haven't chosen yet.)
STILL DO NOT SAVE THE GAME.
10.Go to the Pokemon Center and withdraw your first starter,
and take it's Pokeball.
11.Catch a new Pokemon (Sentret, HootHoot, Pidgey, etc.)
12.Go back to the Pokemon Center and deposit both your
starters into your PC, then change the Box to any other
box. Save the game,
> BUT! <
Turn off the power when instructed not to do so.
(When the 'R' in 'POWER' appears)
13.Turn the power back on. (once again you're standing by
Prof. Elm.)
14.Choose the remaining starter (the one you don't have.)
15.Retraive the others from your PC! Now you can save.

P.S. You don't get Pokedex data for the first two stored
in your PC, but you can fix that by just breeding
those two Pkemon with a Ditto later in the game!