Game Freak and Nintendo released an additional set of Mega Stones to Pokémon Sun and Moon players, not just two but a collection of four Mega Stones. These four must be purchased into Pokémon Sun or Moon through the Pokémon Transporter and Pokémon Bank, while they can also be obtained for free via Mystery Gift. Here's how to get them.
The four Pokémon that will receive Mega Stones are Pidgeot, Steelix, Heracross, and Houndoom. All of them are not often present in Pokémon Sun and Moon, it requires the use of Pokémon Bank and Pokémon Transporter to shift them from an older game. However, this kind of change does not let Pokémon hold items, that's why players can't just bring older Mega Stones.
Here are the Nintendo-provided instructions to get the four Mega Stones.
First, you must select the "Mystery Gift" on the main menu then tap the "Receive Gift." After that, choose the "Get with Code/Password," and then click "Yes," and another "Yes" for Internet connection. For the password, enter "AZUL" and observe as you receive the Mega Stones. Talk to the deliveryman in any Pokémon Center to get your Mega Stones. Lastly, don't forget to save your game.
Currently, there is no specific date from Nintendo on when will the Mega Stone distribution ends. However, Nintendo could probably end this anytime, so it's better to obtain these Mega Stones as soon as possible.
In previous events, some of the Mega Stones became available to Pokémon players, particularly those who joined the live tournaments. For instance, Steelixite and Pidgeotite have been free for players who participated in the Kanto x Alola Regional Rumble.
Meanwhile, the current planned Pokémon distribution events include the Guardians Rising Pokémon TCG tie-in event, and Lycanroc will be available at GameStops starting May 15, whereas the 2017 International Challenge May begins on May 17.