I did a search for "Dr. Seuss Cookie" and found the red and white hat on Flickr, but I'm not sure exactly what you mean by a cat in the hat cutter; a cat in a hat, or just a Dr. Seuss theme:
http://www.flickr.com/photos/13665162@N00/215275154/
You could probably just cut this out freehand or make a template to trace around. Try posting this on the cookie forum and see if anyone else has an idea.
Here's another one in the gallery:
http://www.cakecentral.com/modules.php?name=coppermine&file=displayimage&meta=search&search=seuss&cat=0&pos=19&search=seuss
and another one in the gallery:
http://www.cakecentral.com/modules.php?name=coppermine&file=displayimage&meta=search&search=seuss&cat=0&pos=31&search=seuss
Both made either their own cutter or a template.
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