I hate to sound like a smart ass.....well maybe not .But why dont you measure the thickness of your glass with calipers and get one of the same size? I beleive glass for ground glass is 2mm thick. But I could be wrong so please check before you buy. There are a couple of guys in E bay making ground glass so maybe they can help you better. If worse comes to worse you can have 2mm glass acid etched and adjust with shims in your camera once you replace it. Easiest way to do it would be to remove the back, take a tootpick and measure the depth of the GG. make a mark on the tootpick and when yo replace the GG adjust it until it has the same depth. Or, pay someone who knows what he is doing to do it for you..lol...
Later, let us know what happend....