What clients use version number "2" and version number "1" in their block headers? Is Bitcoin Core the only protocol that uses these version numbers? 

Does anyone know what ABC and Unlimited use?

Is there a place where I can see the raw version numbers for each client easily?
Bitcoin clients no longer use version 2 or version 1 in the block headers. Block version is now defined as per BIP-9, and miners use specific bits in the block version number to signal their support for specific soft-forks in the bitcoin protocol. The top 3 bits of the blocks must be 001, so the range of actually possible nVersion values is from 0x20000000 to 0x3FFFFFFF, both inclusive.