I tried FareFlight.com, and used my standard (non-RTW), plain vanilla routing for Sept/Oct: BKK-NRT-LAX-EWR and return, all on UA. The system first said that the flights were invalid, which I knew they weren't, so I just retried the same flights, and the next time, it came back saying UA couldn't confirm the flights. I tried two other reservations systems, and knew the flights were available. Also, no feedback was provided during the lengthy flight selection process.

Perhaps this site works better on pure domestic (US) routes.