Tome of Polymorph: Monkey

Tome of Polymorph: Monkey drops from hozen and monkey mobs as of Patch 7.0.3. Some commonly-farmed sources include:
 * Deadmines
 * Jade Forest
 * Wreck of the Vanguard ( and )
 * South of Honeydew Village
 * Krasarang Wilds: Unga Ingoo
 * Valley of the Four Winds: Kunzen Village ( and )