Players can acquire the Mohawk Grenades by visiting Night Elf Mohawk NPC's camped outside of every race's starting zone. The grenades have five charges and can be re-acquired to your hearts content.
European and Korean players will be able to join in on the fun starting November 24th, 2009. For more details, read the "Mohawk Grenade" FAQ.
(via mmorpg.com, thx!)