Well, I walked up to the shark bar... killed both wenches that were inside and voila... they both had a shard. So while i may have gotten extremely lucky, I really dont think they are all that rare. *shrug*
Much rarer than one every two hours. I've camped the Hungry Shark tavern in Dulak several times for camps of five or more hours and only recall seeing two of these drop in that total time. Had one drop tonight and it rotted. No one in the zone who needed it, and the guy who ran from the Lighthouse in Gunthak didn't get there in time.
I can confirm that it is rare indeed. I've camped in the Hungry Shark also for at least 4 2-hour sessions now and have yet to see one drop. Guess I'll head over to the white Assassin's bar next to see if one will drop there. The chef's are a bit perturbed to see me hanging around there now. "No laddie - we ain'ts got no bloody shard's on our wenches - begone!" LOL