Wait in Inverse battling gives you Dusk Stones? Also remember that Team Flare grunt in Laverre town that's just walking around? After you beat the game he'll give you a Dusk Stone as repentance of Team Flare's Actions. Of course that doesn't help with now.
Also there's a level in the Secret Super Training levels that give you a Dusk Stone once you're Pokemon's Effort Values are max.
Huh, that TF grunt huh, will note.
And I know of the Aegislash training, only got one out of 10 games.
Plus, I already have one that I found in the wild in Terminus Cave.
Well, from the guidebook...
BerriesOran, Sitrus, Occa, Passho, Wacan, Rindo, Yache, Chople, Kebia, Shuca, Coba, Payapa, Tanga, Charti, Kasib, Haban, Colbur
StonesFire, Water, Leaf, Thunder, Moon, Sun, Shiny, Dusk, Dawn, Ever
OthersRare Candy
If you do not have any fainted Pokemon, Inver will give 3 of one something.