The Song of Silence

Two of the mobs required for this achievement [npc=87344] and [npc=87239] are spawned by using [npc=87361].
In order to use [npc=87361] you need to obtain [item=120290].
[item=120290] seems to be dropping from random mobs in Mok'Gol Watchpost.
When you have obtained [item=120290] you need to go to 42,36 and click on [npc=87361] to summon the mobs.

The other two mobs, [npc=86959] and [npc=87234] are regular spawn mobs.
[npc=86959] found @45.6 34.8
[npc=87234] found @43.1 36.4

Hello darkness my old friend, I've come to talk to you again.

"The Secret Meeting Details are dropped by a Mok'gol Pack-Leader." -- Truly

Drops for me every time. No idea why this isn't mentioned here! Many thanks to Truly.