Okay, just an idea I've had, basically a list of all megastones locations. I'll list the ones I have and where to find them, and if people post more I can add them to the list. Please put locations in small font, so if people don't want to see that one it doesn't spoil it for them!
Okay, so:
Charizardite/Blastoisite/Venusaurite: Gift from Sycamore, or if not chosen sold by a guy in the Stone Emporium in Lumiose for a varying price.
Lucarionite: Gift from 3rd gym leader alongside a Lucario.
Abomasite: Gift from abomasnow in front cavern
Aerodactylite: Gift from guy in fossil lab
Blazikenite: Event downloadable from mystery gift
Alakazite: Found in Reflecting cave on B3F. Apparently only accessible post game
Gengarite: Given to you in Laverre City
Kangaskhanite: Glittering cave post game
Pinsirite: Santalune forest in post game -NOTE X ONLY-
Heracrossite: Santalune forest post game -NOTE Y ONLY-
Gyradosite: Couriway town in post game
Mewtwoite X and Y: Pokemon villages Unknown dungeon
Ampharosite: Given to you in Azure Bay
Scizorite: Frozen Cavern behind Abomasnow in post game
Manetricite: Route 16 post game -NOTE X ONLY-
Houndoomite: Route 16 post game -NOTE Y ONLY-
Tyranitarite: Cyllage Gym -NOTE X ONLY-
Aggronite: Cyllage Gym -NOTE Y ONLY-
Gardevoirite: Traded to you in the post game on a Ralts in Luminose cities Southern Boulevard Cafe -NOTE Wanted pokemon can be anything!-
Mawilite: Shabboneau Castle
Medichamite: Laverre City Postgame
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