Skull Longbow

Acquisition

 * Nightfall
 * The Desolation
 * Ancient Elonian Chests
 * Dune Beetle Lance
 * Desert Wurms (hard mode)
 * Realm of Torment
 * Margonite Chest
 * The Battle Isles
 * Isle of the Nameless
 * Zaishen Chest

Drop research is ongoing and can be found here.