You can also try
www.smallparts.com I use the white delrin balls for my action figure stuff, I typically set various sizes on short brass tube posts, and make a gang mold on all of them as a strip mold, then using a jewelers cut to open the mold, and pour up resin balls the color of the wax i am using.
You can check your local plastics store, and get acrylic spheres in all sizes, and try the same.
Small parts sells a variety pack, as well, and carries various different materials for the spheres. I also use the delrin for eyes, so they have multiple uses aside from joints.