Hey there!
The story quest for Suramar released this week leads you into a purple time anomaly field.
The anomaly spawns little purple voidwalkers with very low HP but a normal loot table.
With this enchantment I managed to get a full stack of Felslate in under 10 minutes.
Enchant Shoulder - Boon of the Scavenger - Item - World of Warcraft
-Accept quest and make sure that Khadgar is following you
-Walk into the field and run past Lady Liadrin so Khadgar doesn't unfreeze her (heroic leap, blink)
-If Khadgar starts to talk to Liadrin just run out and abandon the quest
-camp in front of the stairs and kill all the little adds spawing and loot them.
-Win. Just make sure that you have a shoulder enchantment that drops the stuff you need and enjoy