The AS website does not have the capability of booking AS/AA codeshares yet. I have tried repeatedly to book LAS-EUG (Go DUCKS!!!) with a connection through LAX on the AS website but never worked. However, the LAX connection did show up on other websites like expedia or travelocity. If you want to book AS ticket with an AA codeshare try either expedia, travelocity or calling the AS reservations number directly.