May is one of the most popular months and you may be a little late ...
I know for a fact that the resort is already fully booked until at least May 15th
There are two groups in the last two weeks of May
SDC from the 16th>23rd
http://www.travelsdc.com/sdcweeks.aspx
DennyP's WWW from 22nd>29th
http://www.dennyp.com/dennyptravel/quote_request.htm
Check out the above links, they perhaps have some rooms still available