A new worldwide event is happening for Pokémon Sun & Moon. As of now, you can input the code MATSUBUSA into your copy of the game to receive 5 Mega Stones, including Sceptilite, Blazikenite, Swampertite, Banettite and Cameruptite. [Thanks, Serebii.]
The event is currently underway in Japan, North America, and Europe, and there is currently no mention of how long the event will last.
Pokémon Sun and Pokémon Moon are available for the Nintendo 3DS.