Rainbow Kids has a special needs section which can be found here!
They have about eight kids with Arthrogryposis (or other similar joint disorders) listed.
Here is their section on Arthrogryposis: http://specialneedsadoption.rainbowkids.com/Arthrogryposis_-_Joint_Disorders.aspx
Click "waiting children with Arthrogryposis" on that page and you'll be taken to their listings. You have to register and login before you'll able to see the listings