It may be hard to get that identical shade, but there are a number of online stores that carry glass shades and you could buy a pair. I was recently looking to replace a broken shade, and found this place: Glass shades

Here's another: Lampglass

There are other such stores that you can find through a Google search, and eBay is a good place to browse for this sort of thing, too. Even Home Depot has a pretty large collection of glass shades on its web site. Lastly, local lighting fixture stores often carry an inventory of glass shades.

The main issue is the size of the opening at the top, and the mechanism that holds the shade in place.

I have had luck finding replacements at second hand stores and at restores ( habitat for humanity shops). Just make sure to measure the opening properly. There are many places online also were you can order a matching pair.