Ch'ktok drops these in Paludal Caverns at near 1350, 450. He's got a placeholder of a shiknar and it's extremely rare to get him to pop, let alone drop anything useful.. good luck to all that seek these heavy arms.
I tried for several weeks, several hours a day to get the named to spawn and never did get him to spawn. So, either Verant got this fixed since I tried (which was several months ago) or the spawn is so rare as to be none existant. At any rate, I gave up on it.