A possible alternative to RamShok and YSS, both of which are getting a bit pricy.

https://www.ebay.co.uk/itm/235217867056
https://www.progressivesuspension.com/

US members may do a bit better than that price because of the $/£ conversion scam. I sound a note of caution because Progressive went down the pan a bit in the late nineties and I was not impressed with the (then) bloody expensive pair on the back of my Honda CB500-4, but they've had two decades to sort that out.

It may be worthwhile to go back on the forum to see what users are saying about the Progressive rear shock.  I can't remember the reasons, but I seem to recall that they are not the most highly rated option for the K bike, but I could be very wrong.