Hi Argyrhs, The place that readily come to mind is Newport Optical located in Stanton in southern California. They sell glass for Newtonians, refractor kits, all of the abrasives, etc. They have mirror kits from 4.25-inches up to 18-inches. Their 8-inch mirror kit comes in two types and prices. One is just a flat piece of pyrex and the other has a machine generated f/8 curve to the optical surface, saving a bit of grinding time. Here is the link to the site. http://www.newportglass.com/ The other day I checked on a 20-inch mirror blank and the price quoted was $1,375.00. Thats not bad considering the current buying power of the Dollar. Anyhow, hope this is of some help. -Fred