If at some point you did wish to create a new panel, black phenolic 'Tufnol' would I think be an acceptable substitute for Ebonite.
There's a family firm in Hull who supply an extensive range of plastics and make plastic fabrications for industry. The have an eBay should where they sell various thicknesses of phenolic Tufnol sheet in various sizes. No connection other than as a satisfied customer - I've used them several times over the years.
This is just an example - 200mm x 100mm of 8mm thick sheet:
https://www.ebay.co.uk/itm/360897586...8AAMXQjq5Q-9lI
If ever you did need any sheet, your best bet would be to either drop them a line specifying your requirements or give them a call to discuss:
GFG Plastic Fabrications Ltd,
Nigel John Gray,
Bridge works,
101 West Dock Street,
Hull.
East Riding of Yorkshire
HU3 4HH.
01482 610110.
https://gfgplastics.uk
Hope that might help.