If you try to buy tickets for a special ticketed event and the date says “not available”, that date is sold out. Don’t expect Disney to suddenly drop more tickets for the evening in question. Some people have had luck calling Walt Disney World. Others have asked at Guest Relations on the day of the event. Most likely, though, you’re out of luck. Special ticketed events have a limited number of tickets sold, so it’s important to buy your tickets as soon as you know your dates if you want to attend.