here is something I've never come across before, a semi-fretless banjo https://www.wgfhowsoninstruments.co.uk/custom-banjos/2-11-semi-fretless-sapele-banjo

The Mountain Banjer looks more like a traditional fretless banjo:
https://www.ballardbanjers.com/pricesstandard-models.html

Deering now makes a modern fretless model, similar looking to the Grafton model and cheaper than the Ballard banjos.

I'm simply searching UK pages and I;m surprised to see how many makers are now producing fretless models; have you tried doing the same for germany and adjacent countries?