If you ever find yourself in need of a ground glass for one reason or another, like I have recently, here is the quick DIY solution I have been using.
Get yourself a sheet of mylar paper. I use 3.5 mil paper which is regularly used by engineers and architects. If you can’t find any in a store, call up a local firm and ask them who supplies their mylar. You might even talk your way into a free scrap cut sheet if you try.
There are two sides to the paper, a glossy side and a textured side. Cut to size and place the textured side toward the lens and tape it in place.
Viola! Now you can turn your 35mm into a field camera of sorts. Or you can use it to adjust and check the focus of your lens.