Mysterious Shell

Prior to Wrath of the Lich King, Mysterious Shells were the second most powerful type of bullets available, adding 46.5 DPS.

Source
These bullets were sold for outside Karazhan and also in the Aldor and Scryer sections of Shattrath City. Aldor vendor: Marksman Bova (located in the alcove next to the Aldor elevator). Scryer vendor: Archer Delvinar.

They required reputation with the Violet Eye faction.