Sry for the late answer I was working. ^^
First day 10 hours with ak6 and nothing happens.
Next day picked up Ak7 and farmed about an hour and it dropped.
Oh and if it helps anyone I did all the mobs in Putricides lab in blood spec.
Just wanted to mention that if people where wondering if they could loot it from the boss if they where in any other spec besides unholy.