I think your right, Tim. It's definitively East-African. But are you sure about Nyamwezi ? Could also be Gogo. This tribe has a vast array of clubs.
Here is one that also comes from the same region, but I don't know from which tribe (probably also Gogo).
This is probably some kind of ceremonial club, although it's heavy enough to deliver a painful blow.
A lot is written about African weapons, mostly about the iron work. A good book only dealing with wooden weaponry from Africa would be welcome.