I have 3 pieces of this set.
And I also did a little math - simple one.

This is how many runs it took me to get my 3 pieces:

Shoulderpads - 2nd run in Sethekk Halls
Handgrips - 4th or 5th run in Black Morass
Leggings - around 15 runs in Shadow Labyrinth


This is my speculation:

Helm - about 32 runs
Tunic - about 64 runs

Thats jsut my guess, I'd like to hear from someone who has the full set if my guesses are correct.