Good luck calling because I got the voicemail run-around when I called. Eventually I got to the right place though. If you go to Disney destinations, WDW, parks and look up special events you can find it and buy tixx that way, but I prefer to speak to a person.
I saw somewhere that you get a photo with your admission to the party, but I can't remember where I saw it. Is that one photo per family or per person?