If I am choosing Charmander as my starter, will I be able to buy the Charizardite Mega Stone again? So I could buy another one and trade it to someone else.
I just found this site and it says: "You can always try trading for them, of course, but, because each game contains just one of these items per playthrough, you'd have make a pretty persuasive offer."
Or here which says: "If you didn't get it from him, you will be able to buy it from a man in the Stone Emporium in Lumiose City in the postgame." I'm not sure about the if here.
I want to be 100% sure about this. It sounds like you wont get the Mega Stone of your Starter twice.