Jim, start with MY 55+ community by checking
Imperial Bonita Estates, and if that doesn't work for you, look at my former posts (Oct. 21, 2015) for the list of campgrounds in the SW Florida area. Phone numbers are included for each. Fort Myers RV Resort on US 41 usually has a spot and is a good central area for exploring other possibilities. I personally would avoid Calusa Cove and McGregor. In my opinion, those two are neither resorts nor campgrounds and therefore are not on my list.
On the bright side, the current value of the Canadian dollar has resulted in more open spots -- even one or two here at IBE -- and you might find another park in a similar position. Check my list.
By the way, it's 8:30 a.m. and 71° here in IBE; it is 58° in Mission, TX, according to Weather Underground.