Guess the right place to ask would be Panasonic, or Matsushita to see
if there are any parts left in stock at all.
The yellow light are probably steady, if it's not signal red already!

Maybe some local repairshops have something, but the best shot are
probably to buy a used keyboard to have as a private sparepart store.

I have to admit that I did think to do just that, but since I don't have
Technics keyboard anymore, it's not nessesary.

Happy Playing
GJ