Hey Adam, you might want to get your hands on the June 2010 Wargames Illustrated. There is a very interesting article on an African tribe related to the Zulu's, called the Matabele, who's Chief broke away from Shaka, and how they fought the Zulu's, British and Dutch to form their own kingdom in what is today's Rowanda. North Star miniatures just recently released a range of Matabele, which is the reason for the article. Some of those figures could be used as Zulus, and if playing a battle prior to the split between the two tribes, they make excellent related tribal infantry, as they use shields and weapons based upon Shaka's Zulu fighting style. Generally speaking, the only differences are shield color and some warriors wore black ostrich feathers made into a ball as a type of cap denoting their rank. After the split the weapons changed a bit (they look really nasty and deadly with mult-spiked spears and a chopping axe that makes most Fantasy-style axes look like play things), but everything else stayed the same.
Hope that helps!