I would try at Sasol and the other petroleum companies (Chevron is in CT), as well as the mines (AngloGold, Implants etc).
UCT has a nice career prospectus where you can see which companies employ which types of graduates:
http://www.careers.uct.ac.za/downloads/GRADrecruit2011web2.pdf
Also, just Google Chem Eng bursaries and apply regardless. Don't limit yourself to companies that you assume are more "receptive" to white kids.
Couple of points:
1) Many many people start engineering and then drop out or change to something else, so be very clear on the terms of the bursary and how much you would owe if this happened to your son. DO NOT assume he will make it/want to continue studying it just because he is very clever at school.
2) Many students (especially for Engineering) take longer than 4 years to finish. One again, check what the bursary's terms and conditions are regarding this.
3) Some bursaries require you to have finished 1st or 2nd year of Engineering before you can apply. Maybe then the recession has lifted slightly and there will be more bursaries available for him if you can't find one immediately. If he does well in 1st year he'll also have a much bigger chance of getting a bursary.
4) Seriously look at bank loans for studies, you probably won't have to pay for all 4 years as he really should be able to get a bursary somewhere along the line with Chem Eng.