United doesn't fly to JNB, only CPT and only from EWR.
If it's a partner award you seek, your best luck is probably going to be LH or maybe SAA from JFK/IAD.
SFO(77W)/DEN(788) are probably your best bets for NRT. Fly through Canada to save money, perhaps?
ETA: OAL fly nonstop PDX-NRT.