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Without driving your best bet is probably to do it as part of a tour. The nearest you can fly to is Ondangwa (on Air Namibia from Windhoek). You might find public transportation (busses) to Opuwo, so you probably want to contact tour operators in either of these places and take it from there.
The second option is to find someone who's going there in a 4WD and is willing to take you on. Try travel forums (like those on Couchsurfing) to get in touch.