This is just a thought - go to a scrapbook store that has diecuts that you can use in the store and look through their supply. I know I've seen a really cute cowboy boot die cut that was of decent size (might be a sizzix?).
I haven't seen a Santa style boot stamp or die cut, but you might Google "Santa boot" and see if you come up with any photos or drawings that you could print out and enlarge and trace a pattern.
Good luck in finding what you're looking for!