Last summer, I managed to get 2 seats in FC YVR-JNB and back, about 10 months out (others here have done so too). My advice is to be flexible on dates and book one sector at a time (not sure if this means SiN-HKG, HKG-SYD for you) with a forced layover in HKG if that's the only option. If you have an AsiaMiles account, you can go to the CX website and check availability yourself. Again, check 1 sector at a time.