How do I get the missing mega evolution stones in Pokemon Sun?

Question

I believe I collected all the mega stones in the game and I'm still near -- 30 short. How do I get the rest?

Answer 1

The only way to get them is by participating in the Global Link's battle competitions, where they give out certain mega stones for entering and participating.

Source: knowledge

Answer 2

At the moment, the only way to get the missing stones is through online competitions. However, there will be a way in the future to obtain the stones in a few months via giveaways. You can get Mewtwonite X and Mewtwonite Y right now by entering the code M2DESCENT into your game.