As it currently stands, there is only one way to procure Thorium Headed Arrows:
exchanging them via a quest giver in Orgrimmar or Ironforge.
I suggest implementing a recipe for Engineers to create the arrows themselves.
Not sure if this can be implemented, or what the best way to do so would be, but it would be a nice change that I don't think would break the game.
Perhaps the recipe could be a boss-drop or a drop from Knot Thimblejack's Cache.
Engineering Recipe for Thorium Headed Arrow
Re: Engineering Recipe for Thorium Headed Arrow
You could just install a quest turn in helper to turn in Thorium bullets for Thorium arrows faster tho
Re: Engineering Recipe for Thorium Headed Arrow
The point is to give engineers a way to craft the arrows without needing to go to the NPC at all.