This isn't the similarly-named item from Darkmoon Faire, but instead something that was only obtainable during the Scourge Invasion event just before Burning Crusade launched! Thus, it's super-rare and no longer obtainable in-game (unless you want to pay a fortune for it on the Auction House).
Recently Blizzard changed how this item works, from permanently having a ghostly shade follow you, to having it spawn randomly each 15 minutes. But...it is still a fun item and a piece of Warcraft history for any collectors out there.
I will select the wining name on Friday, April 17th. Good luck!