You can find a wide range of splints and braces pictured on this page: http://sites.google.com/a/larsencreek.com/chicken-orthopedics/leg-braces
They also have something that is called a "Chick Chair" that is like the cradle I'm thinking of. You just make it large enough for your particular...
I can think of two things. First it could be an injury to the joint, causing the swelling. It will heal faster if you can put the bird in one of those cradles for a week or so. It could also be the start of bumblefoot which is usually caused by an open wound that gets infected. Based on...