Here's a tool that helps you design your own.
http://www.degraeve.com/favicon/
After you're done, you can add the file into 'Design | Additional Files' to upload the icon to your site. Add the following before the </head> tag in your overall layouts:
<LINK REL="SHORTCUT ICON" HREF="http://www.yourwebsite.com/acatalog/favicon.ico" />
Obviously changing the http://www.yourwebsite.com/ to the URL of your web site.
Note, if you have changed the 'Online Store Folder Name' in 'Web | Network Setup' (v9 and above) then change 'acatalog' to that folder name in the above address.
Upload your site and then browse to the site and the icon will appear next to your address in the address bar.
http://www.degraeve.com/favicon/
After you're done, you can add the file into 'Design | Additional Files' to upload the icon to your site. Add the following before the </head> tag in your overall layouts:
<LINK REL="SHORTCUT ICON" HREF="http://www.yourwebsite.com/acatalog/favicon.ico" />
Obviously changing the http://www.yourwebsite.com/ to the URL of your web site.
Note, if you have changed the 'Online Store Folder Name' in 'Web | Network Setup' (v9 and above) then change 'acatalog' to that folder name in the above address.
Upload your site and then browse to the site and the icon will appear next to your address in the address bar.