There is a small paperback version of The Perfect Shot by Kevin Robertson which is very portable.It is THE classic of what you want. You may well be able to get a used one on **** or even by advertising on a bow site. You will refer to it repeatedly.
Not all animals are present in all countries. The variety in Namibia is much smaller than in South Africa, if you are hunting a place that is not intentionally stocking non indigenous species. Once you appreciate that, there are many types that you do not have to be concerned about, and it narrows it down substantially.
Personally, I find that telling the variety of small antelopes from each other is hardest because there is so little exposure to them and they are more similar by far than the large species are.
I believe that you are going to Namibia...check out a little hard back book "Namibia Handbook by Lizzie Williams" (it appears to be part of a series called Footprint Handbooks). In addition to lots of travel info and maps there are good animal color plates
Steve