There isn't really an official/legitimate site for sold out tickets. Your best bet would be to call the phone line ASAP to see if anything is still available for parties during your trip dates. (Even though it is long distance for you and there is a significant time change, it could be worth it for you.) If you will be staying on site, the hotels have had a limited number of day of tickets for their guests in the past. You will need to ask about this and be at the front desk first thing that morning. You might be able to book a Mystical Spirits dinner package at BB. Someone reported being allowed to add tickets to a sold out party to that package. Beware of sites selling sold out tickets. Disney states that the tickets are not for resale, not refundable, and non-transferrable. Often the resold tickets are part of a scam -- people report every year about getting scammed with MHP tickets from unofficial sites.