Nice find, Tim.
By looking at the head on the handle, I would say Bamileke, Cameroon.
In 'Afrikanische Waffen' by Fisher & Zirngibl (1978), I found a knife which could be from the same origin. The authors identify this piece as Bali (Cameroon).
The author says : 'Cult knife with fur sheath, belonged to King Galega II'
Especially, the part of the handle near the blade looks similar.
Here's a pic :
