There is no central database or listing of that, as each PTO is independent.
That said, it's usually fairly easy to find that info -- especially in Wisconsin, which is heavily PTO -- with a bit of googling. If you pick a town in your area and google "town of XYZ schools" you'll usually find the school department website... which usually has links to school website... which almost always will have a page for the PTO or PTA.
