I just bought some glass for the Mark II today here: http://www.fireglassonline.com
Was the cheapest I could find within the limited time I had to look. Same as the stock glass in terms of quality. Customer service is great too --- I measured wrong (
) and had to call them to change the order so the glass would fit!
Guy said no prob -- he had just boxed it to ship. Said he'd take it out & trim it no prob. Works for me.