Since 2^256 is likely a number larger than the number an atoms in the known universe, better get to crackin' with that abacus or wait for the advent of quantum computers if/when machines capable of doing this come to exist in our lifetimes.
2
256 is not the number of the addresses. Even if you brute force private keys, that are around 2
256, you want to find a collision, not necessarily someone's private key. A RIPEMD-160 hashed address is 160-bits long, which means 2
160. So you're brute forcing this number:
1,461,501,637,330,902,918,203,684,832,716,283,019,655,932,542,976
Since private keys are ~2
256 and all possible combinations of addresses 2
160, then you're trying to find one of the ~2
96 private keys that collide with the same address. So next time you create an address, keep in mind that besides your private key, there are around 79,228,162,514,264,337,593,543,950,335 more.