Some people may hate me for this but.....
Go to the Labyrinth (Malas Gates)  click the crystal pillar and run to the south (do not go in the doors) , follow the path to the west then north to the castle. Run at the center wall you see and it will teleport you inside , same spot  to get out.  You can mark and Gate.
 
The Astro Daemon Quest Monsters are the ones you want to kill , they do hit  hard(ish) with good HP. They are of the Shadowknight Class and will Teleport and Hide when at or around 40-45% HP.  I put one pet on follow and hit Reveal on its nose.. WARNING the astro will attack the pet first mostly unless your standing right next to the spot 
 
Once dead they seem to drop 100% (for now) a black dyed Bone (Astrodaemonbone when added to loot bag with [claim -t )
 
Collect 12 (longer spawn time but 3 can be up at once) Bones (stackable too !! ) and drop them on Lord British in quest castle.  For now you get a full set of Astro Daemon Bone Armor
It rivals a lot of the better artifacts 
 
Good Luck and Happy Hunting 
 
 
 

Wow, Thanks for posting this!  I did not even know this quest was available.  From looking at the gear it would upgrade a lot of my armor slots.  I know what I will be hunting this next week (once this nightmare of a work week is over with).