If you select change icon for any of these, Windows loads up a dll (I think it's a dll) full of them. You should be able to find the path in the explorer bar. IIRC, the file is in System32\Icons.dll, but I could be wrong. I haven't looked in Seven yet.
Correction. I forgot I was on a Win 7 machine, so I looked it up. This is the correct path for the system and folder icons: