I found some gold matte board at a local framing shop that's a decent color for this set. I glued some foam insulation around the back of the opening and cut a new clear Lucite cover to put in front of it. Not perfect, but it looks reasonable at normal viewing distance.
The new mask's opening is the same height as the old piece of cardboard that I found, but I brought in the D sides to cover the CRT edges. Making a symmetrical pattern and cutting it cleanly was more difficult than I expected!
I'd still prefer to have a factory original, but this will do in the meantime.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html