Do you have a specific area in mind? Contact a local realtor in the area you are looking into and they will have some insight for you and do a full search. It's hard to think about summer in the winter, but you are smart to start now as they do book way ahead of time. Good Luck!
There are a number of rentals that should be coming into our firm right after the Super Bowl. Finding a Spring Lake rental with a pool is not an easy task but can be accomplished. Please let me know if I may be of assistance to you.
I am the rental manager of Diane Turton Realtors, Spring Lake. We will have rentals available with a pool next summer, but there aren't many. Most will only rent to families. If you would like a list of a few that have been available in the past, but will not be guaranteed to rent again next summer, message me. Let me know who the 12 people are, including ages of any children and how much you can afford to spend. The large houses with pools usually run about $10K/week.