Tricia,
Depending upon who you work for it may be better to fly down to East London or Port Elizabeth and then hire a vehicle once you are there. It may depend on your timescales as its about 500 miles from JNB so a lot of time spent just driving. Try using SA search engine www.ananzi.co.za or www.eastlondontourism.co.za to look for info on game viewing etc
Paul