Folder Icons

I'd like to add custom icons to some of the subfolders in my Documents folder, similar to the Music, Videos & Pictures folders. I know how to achieve this, but I'd like the icons to match the style of the Portable Apps built in folders, but I can't find the source for the icons that are used.

I was going to replace the icons in \PortableApps\PortableApps.com\App\Graphics\WindowsFolderIcons with my own so that I could achieve a consistent style but I'm not sure whether any subsequent platform updates would overwrite my custom icon set, and anyway, I quite like the built-in folder icons and wanted to create my own that would match the existing style.

Can anyone point me to where I might find the source files for these icons, or alternatively, at least a bare folder icon without the individual overlays?

Thanks