I don't think they are available yet. Instead, many of us are using furniture sliders. You can pick these up at a home improvement store for about $12.00/4 pack.
It is my understanding Cathe will be selling gliding discs sometime in the near future. If you don't want to wait, I bought my discs at http://www.power-systems.com/p-4117-gliding-discs.aspx. You can get them for either the carpet or hardwood floors and they cost me $14.95 for a pair. I have hardwood floors and nothing else seemed to work as well. I noticed a difference immediately when I started using these. Up to that point, I really did not like the exercises with the paper plates, but now they are some of my favorites.