Tickets for MNNSHP went on sale in July if I'm not mistaken. We're actually going to the party on the 25th and just checked my email history and purchased them mid-July. Tony's does have limited hours (5-8:30) and Seeing as it's right on Main Street I'm sure it was booked quickly with people hoping to get outside or window-seat tables. As it gets closer (especially a day or two before) check back because I think you'll find a better chance of cancellations.
I've never had glitch issues with ADR's but that's not to say it doesn't happen. I did a search for you and other restaurants in MK have availability that night so don't give up hope!