Dolly pet shops on Etsy
Iplehouse sells dogs, panthers and cats. But there are some artists who make and sell wonderful little creatures, both furry and jointed. If you want to buy a pet for your doll, you might find something here:
And of course there are a lot of Chinese fake fur pets on Ebay. They are cheap and almost in scale, and if you just want a cat as a prop somewhere in a picture you will probably happy with one of those.