Okay, thought I'd set the record straight on these drops. Make sure to check the other drops for this quest on this site because I've posted on each one.
The "Crystal of Yearning" only drops from Noc's in MPG. I have gotten 3 of them on noc's only. It is not zone-wide. The guy who said these drop in RSS is confused, he is thinking of geldarian essence which looks just like this item.
The best spot to farm these is the north area in MPG near Girplan Scavenger and Bloodluster Zieh, that entire little stretch is almost all nocs,kyvs, and ukuns and is the area most dense with nocs.
GL, took about 120 nocs to get the two i needed, then one dropped on the way out.
Bezelek <Vigilium>
92 Monk
Tunare