A new event is officially underway around the globe for Pokémon Sun and Moon players. This event gives the Tyranitarite, Abomasite and Manectite Mega Stones for Tyranitar, Abomasnow and Manectric, respectively, as well as the Mega Stone Aggronite for Aggron. These are received via the special code SABLEVOLANT. There currently is no end date known for this distribution, so be sure to get it while you can. The first three of the aforementioned Mega Stones were initially made available as a prize for participating in the 2017 International Challenge May Online Competition.
Source: Serebii
Pokémon Blog 
One thought on “All Pokémon Sun and Moon players can now receive Tyranitarite, Abomasite, Manectite and Aggronite Mega Stones with special code”