Wand of Lightning Shield

Allows the Hero to cast Lightning Shield on a target unit. Lightning Shield surrounds a unit with electricity, dealing 20 damage per second to nearby units. Lasts 20 seconds.

Source
Thrall can find one in Landfall, chapter 1 of the Warcraft III orc campaign, The Invasion of Kalimdor.

Tyrande and Furion can find one in Brothers in Blood, chapter 5 of the night elf campaign, Eternity's End.