As far as the back section coming apart, it doesn't. You can pick up a fiberglass repair kit at just about any auto parts or hardware store. It's pretty easy to use. mend it, sand it and repaint the whole top.
The window is going to be a little harder to find. I know that there are a couple of places where you can find replacement parts like that, I just can't think of the names. Hopefully someone will chime in on that. In the meantime, you could get a piece of lexan cut to fit at a sign shop.