I have an unlocked Galaxy Nexus and I don't see any system updates in settings. Do you have any sources for this?
Manual download link: http://android.clients.google.com/packages/data/ota/google_n...
Instructions: http://www.androidpolice.com/2012/11/13/android-4-2-build-jo...
The OTA was released this morning (I've flashed my unlocked Galaxy Nexus to 4.2).