When do you get gardevoirite in alpha sapphire?

In Pokémon Alpha Sapphire, you can obtain Gardevoirite after defeating the Elite Four and becoming the Champion. Head to Steven's house in Mossdeep City, where you'll find a woman in the backyard who will give you the Mega Stone. Make sure you have a Ralts, Kirlia, or Gardevoir in your party to use it.