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Assuming you are looking for CX's availability - just login to your Asia Miles account, go to https://www.asiamiles.com/am/en/redeem, and then click on the link in that page about reward redemption. It will take you to a page that asks for class, departure and arrivals cities, dates, etc. Submit the information and it will show what option you have.

I also recently noticed BA's Executive Club website (BA's frequent flyer program, same as CX's Asia Miles) is useful to search for OneWorld reward with BA, CX, KA, and JL. You can sign up for BAEC membership for free at ba.com.

If you don't mind sharing the number of miles you have and the route you want, a lot of FTers are actually willing to give you advises to max out the advantage.