Trying to get some Thunderstones.

I already used the one I found on Route 10. Now, I know about the Secret Super Training thing that can give you Thunderstones, but I haven't gotten any from it. People have been talking about the Stone Emporium in Lumoise City selling Thunderstones, but they only sell Fire, Water, and Leaf stones for me. If anyone knows how I can get Thunderstones from the Stone Emporium or some other way, that would be greatly appreciated. EDIT: I have beat the Elite 4, completed the Looker Bureau, and I leveled up my stylish level pretty high.