Rubbermaid (they own Ball and Kerr) won't sell jars to us any more, so we are out of most of the popular sizes. They are usually cheapest at Target or Walmart. When we can find the less common sizes, it's often at Ace Hardware or a local hardware store. Grocery stores also often carry jars.
Jars are heavy and expensive to ship - we would prefer you buy them in person. But sometimes you just want one jar instead of a whole case, or your local store doesn't carry the size you want.
Glass jars cannot be shipped internationally.