When prospectors find these things, they're likely to exploit them independently
One problem with this whole line of thought is this, if I mine a material out of the moon, return it to earth and build a product out of it, I can't then legally sell it because I didn't own the original material. The United States signed the united nations 1967 moon treaty, the material I mined out of the moon is the common property of all mankind.
How can I sell it?
I repeat: developers are more likely to exploit those resources independently. The Moon Treaty is probably another political reason why this would occur.
To simplify, this is how you sell it: you mine the ore yourself, you make the ore into a useable product, then you sell the product (which you, having worked and refined, now own) to whoever you want.