I’m not aware of anyplace in Zambia that has ever had Nyala. Damn good leopard hunting though. And I’m pretty sure that leopards are still closed in South Africa, or at best only a tiny overall quota. There may be somewhere in Moz that both can be hunted together, but none that I’ve heard of. Coutada 9 has excellent Nyala but almost no leopards at all. Don’t know about the other Coutada’s, though 14 might have both. Good leopards in Niassa, but no Nyala. As far as I know, SE Zim is the only place where both can be hunted together. But, I could be wrong.I would second what CAelknuts recommended above. You are almost certainly talking Zimbabwe for that combination. Of course there are other locations but more isolated. There are good nyala in RSA, but leopard is difficult there. A few places in Mozambique to consider, and probably Zambia as well.
Bill