Up to this point, we've only seen official CM 10.1 nightlies show up for the Nexus 4 and Nexus 10, but an unlikely device just got its first taste of Android 4.2: the original Galaxy S (I9000). The builds are currently marked as "experimental," so if you're looking for something stable, this probably isn't the best direction to go.
It could oftentimes be unstable and not properly tested, lacking any changelogs, but eventually evolving into alphas, betas, release candidates, and finally stable releases.
Still, if you'd like to give Android 4.2 a shot, here's your chance. And of course, don't forget to flash the latest GApps.