(Cont.) Gardevoirs and Gallades, alongside several other sapient Pokémon (like Lucario, Bisharp, Machamp, Gothitelle, etc...) once ruled the earth and had civilizations. Eventually humans rose to power and out competed them for territory and resources. The final straw was when humans developed the first primitive Pokéballs and Pokémonkind couldn't develop a counter. The remaining Pokémon (the ones who weren't basically animals) were either forced to accept servitude or driven into hiding. The hidden, mythical villages of Gallades and Gardevoirs are the remnants of those past civilizations.
Gardevoirs have a strong storytelling oral tradition, supplemented through psychic image transfer. They speak of legends from times immemorial where they were created alchemically to serve a Master against a "great evil", and then their Master rewarded them by enslaving them, so they revolted, and before dying their Master created humans as a final curse, so that humans would eventually dethrone them from the world.
While there is archaeological evidence to support the theory of ancient Pokémon civilizations, the creation myth told by Gardevoirs is unverifiable. Some have theorized this is why Gardevoirs and Gallades in captivity bond so easily with human master and become devoted to them, it may be because they were originally created as a servant race and traces of this remain in their subconscious.>>36214200
In my headcanon evolution stones are a rare but renewable resource created through magic, so there's no risk of running out. There may also be other ways to evolve into a Gallade that don't require a stone, but they're virtually impossible to replicate in captivity so a dawn stone is pretty much the only way to evolve a male Kirlia into a Gallade. >>36214277
I like the idea of the Mega Stones being inherited. Maybe have them be alchemical creations from an age long lost, and the knowledge to make more has disappeared.