[Taiki]

Did you choose the fire starter? Apparently at the end of the game, your rival friend Shauna gives you the first form of the starter she chose, so she'll give you the grass one if you picked fire.

I chose fire and my brother chose grass. He started his file over a couple of times to get all the Kanto starters with the Mega Stones so he gave me one of his grass starters but I still don't have the water one. D: Also you can catch the 2nd forms of all the starters and Kanto starters in the Friend Safari if you have friends that are the right types.