There are many sites where you can post for sale listings. There are also a number of brokers, like The Timeshare Store, who will handle the listing for you. I bought one of our Marriott properties through The Timeshare Store, but it was an Orlando property.
Try TUG, as posted above. Ask for recommendations for brokers who specialize in that chain or location. Tom's folks have been helpful to me when I have been looking for a property in another location. They have contacts they can refer you to.