There was a guy in the USA who did make them for the k3 as they are different to the earlier 500/550 due to the horrible PD carbs. I did get some a few years ago, and did keep a note of the website but just tried it and it is no longer there. The name of the website was classicmotorcyclesolution.com I seem to remember it was a small operation so may have stopped trading, perhaps someone on the US sohc forum may know?