The official Pokémon website has revealed a code for players of Pokémon Sun and Pokémon Moon to receive the Mawilite, Beedrillite, Audinite and Medichamite Mega Stones items needed for Mawile, Beedrill, Audino, and Medicham to Mega Evolve during battle.

Mega Stone Power Times Four

Add four more Mega Stones to your Pokémon Sun or Pokémon Moon game. Increase your stockpile of Mega Stones in Pokémon Sun and Pokémon Moon and give more Pokémon the power to Mega Evolve with a special code. When you enter the following password in your game, you'll receive Mawilite, Beedrillite, Audinite, and Medichamite Mega Stones, the items needed for Mawile, Beedrill, Audino, and Medicham to Mega Evolve during battle.

Mega Stones password: INTIMIDATE

These Pokémon aren't available in the wild in Pokémon Sun or Pokémon Moon, but you can bring them into Pokémon Bank via Poké Transporter from earlier games. Pokémon will lose their items in the process, so this is currently the only way to get these Mega Stones in Pokémon Sun or Pokémon Moon.

To get the four Mega Stones:

1. Select Mystery Gift on the main menu.
2. Select Receive Gift.
3. Select Get with Code/Password, then Yes, and then Yes again to connect to the Internet.
4. Enter your password.
5. Watch as you receive the Mega Stones.
6. Speak to the deliveryman in any Pokémon Center to pick up your Mega Stones.
7. Be sure to save your game!

Enjoy bigger battles with the force of Mega Evolution in Pokémon Sun and Pokémon Moon with these awesome Mega Stones.

Source: http://www.pokemon.com/us/pokemon-news/mega-stone-power-times-four/