There used to be a way if you booked online at CX.com which generated an Amadeus PNR. You were able to see the PNR in the URL when you went to view the booking. With the new CX website this "feature" seems to have disappeared.

You can also view your booking if you are an Asia Miles / MPC member and have your number in the booking.

This was precisely this question that googled me onto FT just over a year ago. Never did find a way to do this but I found FT and have never looked back

ExpertFlyer will allow you to view seat maps for CX flights