For a long time there have been rumors that Denn the Orcavoiced dropped a harp called the "Dream Harp" that gave Lullaby +2.
If this harp really exists, it would seem that the Dream Harp is named differently in the English version and does not drop off of Denn (Sea Serpent Grotto).
For what it's worth I killed that NM the other night with no drop of this sort. Well, actually my 75 mnk friend killed it while I cured him a little. But still no harp either way :)
i did some checking on dreamharp seems that it only existed in beta and they removed it from the game after because apparently it gave BCNM people too much of an advantage