You can get the regular evolutionary stone(not mega stones) in the Stone emporium in Lumoise city, find them scattered around Kalos, or find them via Super Training, the extra levels. You're Pokemon must be FULLY eved trained to unlock these stages and do them in time, you get an evolutionary stone for that level. Each extra level gives out different stones.
Mega stones are scattered around Kalos, some can only be unlocked after you beaten the game and its 7-8 pm.
Hope I helped!