In central Hoenn you'll find Mauville, the place that kind of serves like a hub of the game. Considering it's in the center of Hoenn, it kind of has to be.
In the surrounding areas of Mauville and in Mauville City itself, you'll find the Mega Stone's for two very different Pokémon.
One Pokémon's Mega Stone will take you to the see and the other will have you looking for a man in a black suit. The man in the black suit might sound easy to get to, but it might not actually be so easy — considering there's a lot of running around to do.
Mega Beedrill | Beedrillite
The beginning of the game is where you will find this Mega Stone, head over to the Sea Mauville storage room.
Mega Lopunny | Lopunnyite
Gain access to the elevators in Mauville City by speaking to Wattson (he's around the middle of the city). Go to the second floor and speak to a man in a black suit, after that go about your business, speak to Wattson again and then go back to the scond floor to talk to the man in the black suit.
Here's where you can find more guides for catching legendary Pokémon and finding Mega Stones.
