In Reborn,
Mega Ring event is implemented in the game but not yet accessible( Probably in ep 17). The mega stones available are-
Heracronite:
visit Nyu's house in the North Aventurine Woods without any other candy in your Bag other than Blue Moon Ice Cream, talk to him and he'll offer you a choice of either Heracronite or Pinsirite for it (repeatable to get both) Pinsirite:
visit Nyu's house in the North Aventurine Woods without any other candy in your Bag other than Blue Moon Ice Cream, talk to him and he'll offer you a choice of either Heracronite or Pinsirite for it (repeatable to get both) Banettite:
exchange a Floral Charm for it in a house Ametrine City, to a girl complaining about her necklace (possible only after visiting Blake's apartment Abomasite:
Ametrine Mountain B3F, start by reaching Ametrine F1 by climbing up the Waterfall in Celestine F1 (Celestine Cascade entrance) or jumping the ledge and climbing down the Waterfall in Ametrine F2 (Calcenon/Route 3 and Route 2 entrance), open the ice-Strength puzzle by pushing the boulder from one side of the Waterfall and going through the path from the other, go through the Dive spot and through the cave opening at the right (surf over it downwards), resurface to B1F and go to the left in the ice skating puzzle, go into the Dive spot and through the cave opening at the low left into B2F (the Lapras location), go through another cave opening at the bottom left to B3F and find it next to the X Door at the left
Audinite
Azurine cave - requiers surf,dive, waterfall and blizzard
Cameruptite
Crysolia spring sauna
Glalitite
Azrine lake dive, S9
Steelixite
Devon corp, if you've upgraded railnet
IN REJUVENATION NEITHER MEGA RING NOR MEGA STONES EXCEPT HERACRONITE OR BANNETITE