live2fish - With the price of gas, why not just order it and have it shipped? These guys have Dinsmore size 4 shot, and will ship it for $5.50. Yeah, I know it's more than the shot costs, but so would be the gas to drive anywhere that's not real close by. This is probably your best bet:
http://flyfishersparadise.com/
Hook & Hackle is over in Homestead, but I don't know if they sell shot in individual sizes.......