Tridrone (4e Feat)
From D&D Wiki
At some point you were a three-armed tridrone, and have retained their ability to hurl multiple thrown weapons at once.
Prerequisite: Modron, Wisdom 13
Benefit: You may wield a heavy thrown weapon in addition to whatever you have in your main hand and off hand. If you are wielding three heavy thrown weapons and make a ranged attack in the first round of an encounter, you may throw all three weapons granting a +2 bonus to your damage roll if you hit.