Just droped for me from a Temple guard (non elite) 5 mob i killed from zone in from grey. in the first hallway from when you zone in (the one that has a door to the right and straight ahead...It dropped off the first mob after the door that straight ahead not the door on the right in the hallways...hopethat helps maybe i just got lucky
Info was a lil iffy as to where the Elite Guard and Arch Arcanists were, but easist thing for us was take the first "tube" up to 2nd level and they are surrounding the exit area. Multiples dropped first few mobs killed there that were Elite or Arch. G'luck
These seem pretty common. Went to explore Comm 1 and in 3 clearings of the room had 5 Elite Temple Guards spawn. All 5 dropped the cortex. Either very lucky or the droprate was increased. These dropped 19 December 2004.