IIRC, your travel period is during peak summer vacation in Korea as well as the Korean "Thanksgiving" in September when Koreans from all over the world return to their homeland and pay respects to elders and ancestors.

Keep checking OZ and KE websites. They may offer specials, though loads are expected to be full during this period.

Just noticed that you have US Airways Dividend miles. Perhaps you could use these miles to book at least one or two tickets on UA to ICN, connecting through NRT.