In patch 10.0.7.48676 the item " Illustrious Gemdust" was added to help players get Cata Jewelcrafting recipes.
Since then, this mechanic (not the item) was removed from the game.
The NPCs that are supposed to sell Illustrious Jewelcrafter’s Tokens for Illustrious Gemdust are no longer doing so.
It seems obvious that the devs overidded some codes with a pr/comit error or something, and rollbacked that feature out non-intentionally.
Thanks