You're welcome! I just thought of an easier option for a nice vacation from the US…

As West Africa is obviously a bit more complicated to visit, an easier option is South Africa! Johannesburg zoo exhibits many different species not kept in other zoos around the globe (in a very 'enjoyable' setting too!). I guess you don't see these antelope species in major western zoos (e.g. in Europe and N. America) cause they're not threatened or even rare in nature. Some interesting species the Jo'burg zoo exhibits are:
Grey Duiker (Sylvicapra grimmia)
Lord Derby Eland aka Giant Eland (Taurotragus derbianus)
Bushbuck (Tragelaphus scriptus)->there are two species, this one is more related to Nyalas
Red Lechwe (Kobus leche)
Southern Reedbuck (Redunca arundinum)
Further they have the more common species such as Blue Duikers, Nyalas, Impalas, Waterbucks, Common Elands, 3 zebra species, 2 rhino species, Springboks, Bonteboks, Greater Kudus and many unique species of birds, to name just a few…
Have you ever been to the Memphis Zoo? I remember I was impressed by a couple of unique species there! For example, when I visited about 3 years ago they had Yellow-backed Duikers (Cephalophus silvicultor) which I hadn't seen before…