Of course with no reviews, you may not get much interest.

Your best bet is going to be contacting providers or agencies in the Boston area.  I don't know much about ladies who may live and work on Nantucket but I'm willing to bet that there are not many.  You should expect to be asked to pay all traveling expenses and probably a multiple hour appointment and possibly an over-night hotel room. You should also expect to be asked to provide screening information.

If there's time, you should arrange to see someone or a few someones for standard 1 hr meetings, probably at their incalls in or closer to Boston. (1) You'll get to know if they are what you're looking for for the party. (2) You'll go through a "normal" screening and once someone is comfortable with you, they may be more likely to go to your bash on Nantucket.

As helpful as ads and reviews can be, you probably don't want to book a multi-hour romp and find out that the chemistry just isn't there.