I was at first thinking about the .315 balls at cabelas, good thing I didn't get in a hurry and order them.
I did find these .320 balls at dixie:
http://www.dixiegunworks.com/product...bohniproe59ol3
Looks like TOW has a couple of options too:
http://www.trackofthewolf.com/Catego...1/1/BALL-320-X
I'll check the local GS today and see if he just happens to have any .320-.322 balls or some #0 buckshot, if not I'll be ordering from somewhere soon.