I'll stick with 3 possibilities: Judge A. Napolitano, J. Amash and J.C. Watts. However, I think Amash kindly declines the offer, seeing that he's better off in the House, where a potential Rand win would need him in Congress for the tough votes. Just my 2 cents!
I've wondered about this question myself, but I think having Judge Nap on the Supreme Court would be more useful. That's probably what Nap would want anyway.