EDIT: the rude reply above mine has been removed, so that's good. ^_^
Most people who have paw boots/shoes make their own, and actually they're all pretty much like slippers rather than true shoes or boots.
Check out http://community.livejournal.com/fursuit/
for tips on how to make your own. Many types don't even require sewing!
Alternately, on the profile page for that LJ community, you'll find links to places where you can commission someone to make some paws for you.