If you belong to a Trap or Skeet Range, you may be able to piggy back an order for reloading suppiies when the club gets their clay birds delivered. I belong to a Trap Range in New Jersey that gets birds delivered twice a year from a supplier in Pennsylvania. They have pretty good prices to begin with, but they give us special prices when they are delivering birds, and don't charge shipping or tax. I usually buy everything I think I will need until their next delivery.
Also, a lot of vendors show up to the bigger State Trap and Skeet shoots, They usually have very competitive prices. Even if your not a competitor, its worth checking out the vendors if there is a big shoot fairly close to you.