Many restaurants offer "standard" Thanksgiving fare in addition to their regular menu on Thanksgiving. We did 22 people at LTT seven years ago-excellent choice--we had 2 large tables. 2 years ago we had 24 people at Fulton's Crab House which offerred turkey w/ trimmings in addition to regular menu. This year, we have 29 people at Whispering Canyon. They are offerring a special Thanksgiving menu; I'll let you know in early December how it is!!!
For this years reservation, I called group dining 6 months before to inquire about possible restaurants with such a large party. They said due to the size of the party, I would have to go through them but that most restaurants could accomodate us. They also said the reservation could only be made using the restaurants normal booking time frame (120 days for resort restaurants & EPCOT, 60 days at MK). I called at 7:00 am 120 days out and asked to be switched to group dining who made the reservation. I had to leave a $10 per person deposit b/c of the holiday.