In addition to those already mentioned, Empress do a Zulus-getting-shot casualty pack, though no British casualties. The generic tribal casualties in Foundry's Darkest Africa range do perfectly well as downed Zulus, especially if you provide them with shields.
The old Foundry range also has Brit and Zulu casualties. Possibly a little on the small size for today's figures (or possibly not, I might be wrong there - it's just that some of their older ranges are a little on the wee side), but it might not matter so much with casualty figures.
The Foundry offshoot company Casting Room Miniatures also do Zulu casualties. Some of Casting Room's sculpts are pretty ropey, from that dark time when Foundry released quite a bit of dross (which is why, I think they hide them away as a separate company) but the Zulus are actually really, really good for the most part, some of the best out there in my opinion.