Researching the internet, it appears the icons are stored within an .Exe or .Dll file. As such, they are not something you can click on and view, like looking
at a .jpg or .png image.
Your best resource will be searching Google for "Excel icons" and find a free download site that appeals to you. Downloading the file format of .ico
for the icon images will most likely be best. There are free converters on the internet as well that will convert .jpg / .png / .bmp files to .ico format.