I bought a bunch a couple years ago from wholesalecases.com, but looks like they've closed up shop. They do have a link to
www.collectingwarehouse.com on their website, and I checked and they do have protech stands. So you might try them, though I have never personally bought from them.
There used to be a bunch on eBay for cheap, but it looks like stock has dwindled over the years. I guess they're fairly soughtafter now.