This is mostly studios, and from 2015. It over predicts availability and is being updated by the creator, bless his soul.
Studio availability is a good look at 2BR lock off availability as well.
But, in general, unless you do the kind of work Pete did with these charts, there is no way to check what is usually available at different times of year historically.
Busy season is September through marathon, with a few times of super-extra peak -- the first two weeks of December, the last weekend of F&W, the Wine and Dine Half, Jersey Week. (Not Thanksgiving or Christmas, actually!)