https://www.gamespot.com/articles/four-more-free-mega-stones-in-pokemon-sun-and-moon/1100-6453220/

Nintendo is giving away another batch of free items for Pokemon Sun and Moon. Pokemon fansite Serebii has reported that players around the globe can now get their hands on four more rare Mega Stones.

As with previous distributions, players can download the items using a universal code. This batch consists of Mega Stones for Ampharos, Altaria, and the Legendary Dragon-type Pokemon from Omega Ruby and Alpha Sapphire, Latios and Latias. None of these Pokemon can be found in the wild in Sun and Moon, however, so players will need to either transfer them from a previous title or obtain them through trading.