Thoughts:- FT is not a travel agent or award booking service
What research have you done to date?
Which airlines fly to Cancun? Any of these available with Amex MR?
You could try http://www.flyertalk.com/forum/trave...e-reviews.html

At peak dates like yours I would not be expecting much in the way of award availability now. Many would started looking for awards 353/330 days out.
Likewise many would have booked cash fares by now in the lower priced fare buckets.
Others will also planning trips to Cancun with miles and/or cash.

Airlines know late Dec/early Jan are peak times/high demand for travel, especially to the sunshine, so price airfares accordingly.

A some what similar thread bases on Cancun
http://www.flyertalk.com/forum/infor...l#post26751297