Custom dyesub over a PBT keycap

[Cherry1990]

I am thinking to do a custom dyesub print over a PBT keycap.
The keycap is green, I would like to print a black symbol on it.
Any suggestion in Europe? I would like to print 6 keycaps, a very small number.

In case it is impossible, any other suggestion for a custom symbol over a keycap?

Thank you.

P.S.: I have the blank keycaps.