I have managed to find the plugs made by TE Connectivity (of course they are freely available on Bosch cables too) but the sockets are not available anywhere I can see. They are NanoMQS plugs/sockets. They are attached to the internal PCB and the plastic moulding is part of the case. If you were in the game of making speed dongles (hypothetically - I'm not) you would need these sockets.
The idea is to extend derestictor's wires so that it could be installed above the motor in seat tube. Currently it's so tightly packed between the motor and rockguard and the wires are exposed on the rockguard holes. The wires have already scratches.
Another or default option would be using heated shrinking connectors but new connectors would be a little more nice way to do it.
@Hamina how did you get on? Did you ever find those sockets? I'm still trying to hunt them down but no luck. An extender for the speed sensor cable (with plug one end and socket at the other) would be just the thing I'm after.