"Such a law would then make it not worthwhile for ChinaMiner to go and mine Apophis since they wouldn't be allowed to sell anything made from the ore in the USA."
Only in Unicorn Fairyland maybe. In Reality, ChinaMiner wouldn't care less about the US of A , given that whatever Unobtanium it produces that makes the effort of going out to space worthwile, already has a market: the Rest of the World.
The US of A would be welcome to their slag, though. Ballistically if they get too uppity about it.