I have never seen a set of replica R99's for sale, they seem to be one of the few wheels that nobody has had a go at. I could be wrong though.
As far as telling if they are genuine are not goes. Here's a tip.
Check the back of the wheels. They should have the BBS logo (they make them for MINI) and also the word MINI stamped on the rear of the spokes. They also have part numbers stamped on them.
At least mine do, and I know they are Genuine.
Hope this helps.
James.