Camped the Malfunctioning Stoned dudes at the entrance and got all sorts of loot ranging from Blue Diamonds, Noc Claw, Pile Of Gravel, Emerald, Cracked Stone Eye, No Tome's but good EXP
Indeed it is rare, 3 days into the OoW expansion I was exping at the expedition zone entrance with some guildies and looted one of these for my gimp ranged item. Subsequently, I sent it in to Alla's stating it was a rare from yard trash....not common at all. We spent 3 days in RCoD going from 66-69 and never saw another drop.
Our group got 2 of these over about a 4 hour period. One every 100-200 sounds about right, closer to 200. One of ours dropped off a Noc, the other from an Ikaav.