Hi, Gerry. Can't help on a manufacturer but the is a discussion on wainscott heigth not too far down. If you make the height of your wainscott fall under the window apron or remove the apron and run it under the sill, that makes it easy. If you have low windows, you can just butt it up to the stile molding. There are a lot of variations possible, depending on your window height and the height at which you run your wainscott.
As an aside, you might want to consider running flat panels and then some molding in the field a couple of inches in to simulate raised panels. Heck of a lot cheaper this way than true raised panels.