I'm afraid that I'm not going to be of much help, then. :/
I wouldn't have the slightest idea of where to find that set of images, though I imagine you're right and that's exactly how it's handled.
Ahh, yeah, that's true - it can be a pain.
I don't use a windows 8 theme, but when windows 7 was my primary OS, I used to tweak with it a lot. Look at [http://www.deviantart.com/customization/skins/?order=9&q=windows+8]a search for windows 8 in skins and themes[/url].
Another thing that you could definitely consider is using litestep; I don't know if it works on windows 8, but if it did, it's almost infinitely customizable, and there are hundreds of themes for it.