Voigtlander Avus Focussing Screen

I recently got a Voigtlander Avus 3 and a half and 2 and a half (or more simply 63mm x 90mm), and it didn't come with any backs or screens.
I used to have some tarp around, that was great to test focussing on cameras, but I'm all out and there might be better options?

How can I easily make a DIY focussing screen for a Voigtlander Avus?

I made one a while back by throwing away all but the part of a film pack that lands the film at the focal plane and I cut down an old broken ground glass from something and glued it into that piece. Film pack adapters were pretty common with these camera.

Ugly but worked well enough. Nothing holds it in place though and it will fall out on the ground if you're not careful.