Does anyone know who can supply the gas discharge display unit/units in the NARCO MK12D nav/com?

My display is failing hard to se at night , not so bad by day, but has to be fixed.

I see lots of adverts for the MK12D+ upgrade, but would like to start by trying to repair or replace the display panel.

Or buy a second hand unit which I guess can have same problems.

Does anyoen have a link to the repqir manual for the MK12D or part numbers for the front panel displays?

Thanks