Help! :-(

[BarryMead]

I assume that you have already either unsuccessfully reached out to the manufacturer, or determined that the product is no-longer in production.
The device featured in the photograph appears to be a cross between a multi-meter and a calculator. Even displays for popular calculators are very unique to the model number and manufacturer. They are custom designed to have the symbols and icons required for the intended purpose. It is very unlikely that a display for another model calculator, or even another model multi-meter will be compatible with the display of your unique device. The display for an HP-11C would probably work for an HP-15C, but I doubt your multi-meter/calculator is very similar to other products made by the same manufacturer is it?

Sorry I have no better news or advice to give you.
Good luck in your search and best wishes.
Barry