So, the most frequent question I have gotten since posting my BB-8 Pattern the other day, is "where do you get 5 inch doll joints?" I had no idea they would prove to be so hard to find, since I bought mine about 7 years ago.
Anyway, fear not! You can make your own with things you probably already have in your house.
All you need are two disks of some sort, a thingy to keep your wire from pulling through the hole, and wire.
CDs are 4.75 inches, which is close enough to five inches for me! The orange thing in the photo is a giant button, but if you don't happen to have a giant button in your craft stash, I am sure you can find something that will work.
The wire I cut from an old wire hanger, using a pair of needle nose pliers. I could have gone to the hardware store and bought a cotter pin, but what is the fun in that? :P If you have thick pipe cleaners they might also work, the ones I have bend too easily.
So anyway, the only thing left to do would be to install it in your BB-8 and bend the wires down.
I hope this helps you in constructing your very own BB-8!