Minifigs do 4 packs of Xhosa although they are not showing in the new catalogue since Caliver took over.
Eureka do Abyssinians.
Tin Soldier also do a range for Abyssinia but they concentrated on the peripheral tribes rather than the bog standard Abyssinian foot with gun. This does mean that you can get Galla (mounted and foot), Amhara, Bana, Somali/Dankil and Masai.
Irregular also do Masai.
I presume you are not bothered about the Bedouins/Tuaregs/Mahdists?Haddendowa.
Regards
John