Now this is strictly from my own personal experience...but I think the Chaos Sanctuary is "the place". I have found the IK armor there twice...from just random monsters, could have been uniques or bosses, not sure. I use a glass cannon strafer for my MF purposes, so I tend to kill things off screen, and I don't hit the alt key until stuff is dead...so I'm almost never sure who drops what. Also, as a side point, the only golden sacred armor I have ever found was in the CS as well.
Eldritch is my other choice, as he, or his minions, have also dropped the IK armor twice for me.