The Orb of the Sin’dorei drops from Kael’thas Sunstrider in Magister’s Terrace on both Normal and Heroic. However, it is more likely to drop on Heroic mode.
Unlike the Orb of Deception, this does not need to be equipped. While the Orb of Deception has preset gear it disguises you in, this item lets you keep the look of all your current gear. The effect lasts for 5mins. You can cast and attack without breaking the effect. However shapeshifting Druids and Shamans will break the illusion.
I read that BE’s who use the item will just get a new hairstyle. So with our race changes, it appears the same thing happens. I love that we still have our own gear on. Woot for Transmogrification!