I bought the minnie ears with the veil at the World of Disney at DTD for 16.00. I'm not sure how much the top hat was since my DF refuses to wear them. Congratulations on your upcoming nuptials and have a wonderful disneymoon. We're looking forward to hearing all about it when you get back.
They don't sell them at the malls. You can call disney merchandising and they will ship them to you but shipping is very expensive. Your best bet is to wait until you get to the park.
We got married last week at the Disney Yacht Club. My wife ordered ours from the Days of Christmas store at Downtown Disney prior to our leaving. They customized them for us and had them waiting at our resort gift shop when we arrived.