Difficult to size sterling silver. Many silver pieces are bathed in platinum as well to reduce tarnish.

If you contact the Gem Store in Knoxville; they are the service arm of JTV and many un-sizeable items are in fact sizeable.

Sometimes there are side stones and resizing stretches/tightens the prongs or setting that holds those stones and they may loosen, fall out or even break. If you really love a ring and it is not available in your size, order a larger size and get your jeweler to add "bumps" inside the ring to compensate