Pokémon X & Y Cheats: How to obtain Garchompite to get Mega Garchomp
Mega stones! You want 'em! We know where to find 'em!
First, keep in mind that you won't be able to find these Mega Stones until you beat the game and complete a slew of quests to unlock this ability. You can find the tutorial on how to start hunting for Mega Stones here.
This one is a bit tricky to find, as it requires you to venture a little bit through Victory Road. To get through this as painlessly as possible, first Fly to the Pokemon League. From there, head South into Victory Road. Go through two sets of caves until you re-emerge outside on a path that has a bunch of crumbled walls. You'll know you're in the right area by going North and seeing a grey stone platform, where you fought your rival before entering the Pokemon League.
From there, head left until you reach one of the spooky girl trainers and a wall behind her. You'll need Rock Smash to destroy wall and access the area behind it. There you'll see a tower and next to it a shiny piece of Garchompite.
Remember, this must be done between 8PM and 9PM and after touching the Sundial in Anistar City.