Pictures for icons (file-ending ".ico") are usually stored inside installation-folders, beside the correspondending .exe, or in a number of Windows-folders.
You could do a complete search of all icons on your drive by typing "*.ico", perhaps unhidding/unprotecting all folders beforeahead if you want to see all Windows-icons as well, and then pick from this list.
If you want to change them via Paint just duplicate one of these and open in Paint. It can handle the file-format.
