For instructional material, the only thing I'm aware of is a book called Les Secrets De La Basse Africaine (which I don't think you'll have an easy time finding). As others have mentioned, African music is not just one style. The bass you hear in Congolese rhumba, for instance, is very different from what you'll hear in township jive. The music itself is probably your best bet. Have a look here:
African bass lines?
and here:
Lets see some love for Afro-Beat/Afro-Groove
I would suggest you pay particularly close attention to what the drums are doing in various African styles. See if you can find Brice Wassy's instructional book - that should point you in the right direction. In the meantime, do yourself a favour and pick up Jean-Luc Ponty's "Tchokola" album.