their Mega Stones are all event exclusive.

They make them available through the "Get with Code" method like the upcoming Shiny Gengar and Diancie events. Each code only gives you one random Eeveelution Mega Stone so you won't know which one you'll get until you actually input it into your game and you also basically wouldn't have a choice of choosing which Mega Stone you'd want.

I can only imagine the madness that would ensue from this.

Who else would lose their shit if this happened?