Hmmm, they used to have them with a "buy it now" price of $20. Here is all I found for them now LINK.

Here is another option for you LINK. They look like the same rings but are at a $19.99 "buy it now" price. Good luck, and let us know how it goes. I'm not sure about the ones Tom linked, the pic shows the wrong shape. Make sure you get the aluminum ones whatever you do.