There are some lists out there that will give you historical deals - this will give you a jumping off point BUT there is no guarantee that the deals will be released. It also seems that the resorts for the deals tend to change quite often ( meaning not all resorts are included in all deals ).
We did use the historical rates from the last few years to find out when free dining would be released. It was within a week of the prior year.
We did not wait to book until the deal was released. We booked the resort and wanted and got lucky that it was part of the free dining this year.