With the update of Pokémon Bank on January 25, many Pokémon that were not previously seen in the Alola region are making their way to players’ Pokémon Sun and Moon games. The Pokémon Company has received inquiries from players curious about how they can obtain Mega Stones for their Pokémon that were brought over from different Pokémon games via Pokémon Bank. Mega Stones are powerful items that greatly affect the trends of battles between Trainers. As a result, we have decided to start giving out these otherwise unobtainable Mega Stones as participation prizes in Online Competitions. We hope that as we gradually introduce these Mega Stones, players will enjoy seeing how trends in the battle environment change over time.
To begin, Mawilite and Beedrillite Mega Stones will be given to those who participate in three or more battles in the 2017 International Challenge February Online Competition. The Pokémon Company will continue to update players about future opportunities to obtain Mega Stones, so be sure to stay tuned.
Source: Pokémon Global Link
Pokémon Blog 
This seems like a wonderful idea! 😉
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