Postcards are sent randomly. The way I figure it just get on every single disney mailing list, and you will eventually get something. I was lucky enough to get a email for our last trip.
The stipulation (sp?) about these postcards and emails are they have specific codes on them and are only good for the recipient. Basically it means its NON-transferable.
You can always call CRO and ask if you have any codes attached to your name. If say you lost your postcard or trashed your email, they would have a note in the computer saying that they sent one to you.
Sorry the news isn't the best.
But good luck planning your trip!