Don't need anything one them, just a flat circular piece of glass.

Hi Jack,
I can't remember the name of the supplier but when I needed a flat circular piece of glass I ordered it from a clock parts supplier on the internet. Reasonable price and they had a lot of different sizes.
Sandy

Maybe you can borrow a circular glass cutter (I can't be the only one who has one...). You could probably make one: a foot ruler, suction cup, a standard glass cutter and some sort of clamps to hold them together. Might take a couple tries, but then thrift store framed pictures can provide a lot of cheap glass.

Any glass business will cut one for you while you wait.

I have used this place for custom glass. http://www.onedayglass.com/

reminds me of a funny story. Went to the craft store to get a piece of oval glass cut, and the guy behind the counter said the glass cutter that cuts that kind of glass was broken. Called the next day, and the guy on the other end of the phone laughed, and said it was not broken, and to bring in the frame and he would cut it for me.