I'm afraid your experience is not unique. There appear to be seats on most flights, but not enough to meet demand for popular routes. You might have ot YVR flights in November, but BKK requires -350 day planning and some luck.

For August, the whole of the west coast will be out, but you could connect in New York, Chicago or Toronto (which would not require you to pass through immigration).

If you don't use the Amex you *might* get the connecting flight thrown in on AA First or there might be an outside chance of getting JFK-YVR on CX. ^