I know this is an old item - but this thing is hardly "common". I spent almost a year kiting in IG off and on - and saw it drop once. Magelo lists the probability of a drop as varying from MOB to MOB, but for the MOBs with the most reported drops, the chance is about 0.05%
I can confirm that this dropped from one of the mastodons near the crotch of the V to the North. Can't say for sure which one, but we were pulling mostly yellow cons to level 71.