I own the Fany Gerson Paletas book that @lemniscate linked to. I have made most of the paletas recipes and give the book high marks. The focus is on paletas with 24 recipes, 12 aguas frescas and 11 for shaved ices. The later may or may not be of interest as cocktail subs.
While I know this is not what you asked for, I listened to an interview with Julia Bainbridge, author of Good Drinks: Alcohol-Free Recipes for When You're Not Drinking for Whatever Reason (eG-friendly Amazon.com link) and thought it sounded pretty good. You can check out a list of recipes here on Eat Your Books.