Advance air ticket reservation

Hello - hope someone can help. I am planning a self guided trip through China and have been able to find all the trains I need, but only a few of the flights. I am guessing because I'm searching too far ahead, the airlines haven't released their flight schedules yet (for early/mid November). Does anyone know how far in advance tickets for domestic air travel can be purchased?

It seems I can only search up to 2 months before departure date.

Looking for Manzhouli - Tongliao (sunday flight). Okay Airways usually operate this flight on a Sunday that I can tell.

Regards PH