Schematic: Arcane Bomb

Source
This item has been found to drop less than 5% of the time from Azeroth bosses:

(As reported by wowarmory)
 * Nefarian, in Blackwing Lair
 * Onyxia, in Onyxia's Lair
 * Lord Kazzak, in Blasted Lands
 * Azuregos, in Azshara
 * Highlord Kruul, in Durotar
 * The World dragons of the Emerald Dream (found in Duskwood (Twilight Grove), the Hinterlands (Seradane), Feralas (Dream Bough), and Ashenvale (Bough Shadow))
 * Emeriss
 * Taerar
 * Lethon
 * Ysondre

Thottbot reports singular instances of this schematic being found as loot from some creatures in high level old-world instances (Blackrock Spire, Scholomance, Stratholme).