that's really wired, if SAN-LAX-NRT has avalibility in W then LAX-NRT should definately have it too, must be some sort of glich in the system. what dates are you trying to book, i gotta check this one out myself.

If i were you i'd just book the flight out of SAN, and do a schedule change on NWA.com within 24 hours of booking, if that dosen't work then call NW and tell them to take out the SAN leg, and make sure they don't charge you a change fee. If it dosen't work now, try again in a few weeks.

And if worst comes to worst and they make you fly out of SAN, then you can book the SAN-LAX flight within 48 hours of the LAX-NRT flight so it counts as a connection, then drive down to SAN and do the flight as a formality, but don't bring any luggages, and when you get to LAX for the trans-pac flight, check the luggages with your boarding pass.