For getting dusk stone from super training:
1. Get a pokémon who is fully EV trained (can only get stones if you have one)
2. Beat all level 1, level 2 and level 3 super trainings (these are the ones that give you EVs) with that poke
3. You'll unlock bonus super training regimens which each give stones as a possible reward.
4. Aegislash gives dusk stones. Higher chance if you beat it faster.