How To Get Second Starter Pokémon:

First you have to beat the game, then you go and catch a Ditto at Giant Chasm. Before you beat the make sure you save the old man from Team Galactic so you don't have to save him after. Then go to the day care center on route 3 and put your starters Pokémon with the Ditto and go from the day care center to Castelia City and back two times and talk to the old man to get the egg. There you get another starter Pokémon. Don't worry I tried this myself it works.