Download the calibre source from here:
http://code.google.com/p/calibre-ebo...-0.8.10.tar.gz
In it you will find the icons in scalable format (SVG) in the imgsrc/ folder. The actual icons are generated from these sources in the png format. The actual icons are in the resources/images folder.
Make your changes, and post them, you will get feedback from users, if there is a consensus that the changes are better than the original, I will be happy to update the icons.
Instructions for getting your calibre install to use customized icons are here:
http://manual.calibre-ebook.com/cust...lates-etcetera