There are almost certainly some others hidden in the game's code that we'll only be able to get through events, like the Blazikenite (or maybe we can find them with Pokemon that aren't currently available in hand).
Creator of Jay's Journey (see quote!) "It's not ten years old! Therefore, it sucks!" - Nostalgia whores everywhere
The odds of them being in the game are slim to none. The actual in-game itself has been gone over by a large number of people, everyone just accidentally missing a mega stone is unlikely.
However, they could very easily do further events like the Torchic one. Mega Blaziken doesn't exist in-game unless you get the event Torchic. Until we actually have successful data mining, we won't know what mega evolutions have already been programmed into the game.