The magic phrase for this part is 'electroluminescent panel'. Apply a relatively high voltage at a frequency that's typically in the KHz range and it glows. If you're lucky, you might find an exact replacement panel. If not, some vendors claim that you can cut the panels to size, but I'd only suggest that as a last resort. A few years ago I replaced a panel on one of my old pieces of equipment. It turned out that the unit used the same display as some popular music synthesizer / piano units. It was a drop-in replacement.
Check the usual sale and auction sites.