In reality you can't get past a 2^256 limit of dev/urandom cspring without introducing your own random number generator which is possible.

But yeah its easy math, lets say the pair is 1,000,000. Thats 1,000,000! possible combinations. You could stack 1,000,000 PB drives across the universe and not be able to store all the unique combinations.

So you demonstrate utility of RSA and ECC by showing how it remains "useful" by appropriating the complete universe to store your private keys? That sounds like a useless (and expensive) scheme, if it costs a universe.