It is almost impossible to substitue a reed from another maker, they just don’t sound the same, even a good accordion repair shop will have trouble with this.
I sent a message to Martin Mauer and asked if he has a Low C reed available, hopefully he has one that he can sell you.
here is his email address and web site
his email address is fewakkordeon-maurer.de
https://www.akkordeon-maurer.de/verkauf.asp?id=3&id2=10&lang=1