I don't think there really is a Republican (US)/Conservative (UK) party in South Africa. The DA is a liberal party, and I don't support their stance on the death penalty. They also support AA & BEE in principle, although obviously they disagree with the implementation of it. The FF+ is too right-wing for my tastes...there doesn't really seem to be a middle ground.
So you would argue that the Republicans or the Conservatives would serve your interests? I find that hard to believe. Notwithstanding that fact that they serve in different countries. But the Republicans and Conservatives do not have cut and paste with search and replace identical copies of the same manifesto. There are differences between the two, so you can't state that they serve your interests (and here we are talking about exactly 100% meeting of the minds).
As has been said, there is enough choice for you to find something that provides the best compromise. Or you could start your own party.