To get Squirtle and Bulbasaur, there are 2 ways to get them.
1) trade from a second gba and game (can be leafgreen/firered). Simply start a new game on the second gba, and select the starter you DID'NT choose on the other gba. Then make your way to the nearest Pokemon center, and go upstairs. Trade it to the other Gba, and start a new game and repeat the process.
2) CHEAT! yeah, you can cheat the game (if you got action play/Vba ect ect)
Hope this helped