I used hionadu's "Stand on Phurzikon's spawn point" method, and this worked quite well. The Respawn rate seems to be 0:1:06, like the Quillmane spawn. Find Phurzikon location on brewall's map, and stand there. Kill all the mobs in that area until a mob spawns on that point. Easiest with someone with a good ranged attack, or two people, one to stand and get attacked by new spawns, and one to run around killing. The different PH's i found at this spot include:
a mouldering gorilla (8)
a tottering gorilla (1)
a scoriae hornet (2)
a forest giant ancient (5)
a forest giant verdant (1)
a sarnak zealot (5)
a sarnak avenger (4)
a sarnak champion (5)
an ember hornet (3)
greater war boned skeleton (6)
greater plague skeleton (2)
wurm (1)
Nezekezena (7)
Phurzikon (5)
The numbers in brackets are the number of times i saw that mob spawn once i started counting. With a 51 Bard/Shaman/Mage this spawn was very easy to manage, even with wandering adds thrown in the mix. The embers eventually dropped from Phurzikon. I also had Healer and Rogue mercs. I really wish the drop rate was better on this item, but all things considered, WAY better than the goblin spawn for cleric epic! Overall i think with the 55 spawns it took to get drop i probably spent 1:15 doing the whole thing, but it was so efficient. Hope this helps anyone else working on this!