I gave up trying to sell the KSports and decided to replace the springs. I found a good source with a lot of information: Swift. They have a lot of options, including thrust sheets to fix that horrible clanking problem.
The rear springs are fine. I only want to fix the front because it is far too stiff at 6kg.

My plan involves 3.57kg or 4kg springs in one of two configurations:
1) 10" long to guarantee enough stroke including preload.
2) 8" long plus assist springs, but not sure what rate of assist springs to get.

Hooke's law shows that a 4kg assist spring with a 4kg main spring yields a 2kg rate until the assist spring collapses: (4*4)/(4+4) = 2

Basically, I am not sure which route to go because I do not have a corner weighing system and I do not have the time to disassemble my front suspension to weigh it and determine the suspension frequency.

I plan on making a decision by Monday.