Convert KCL to SZS

Although both the KCL and SZS files originate from the Mario Kart video game developed for Nintendo Wii consoles, it doesn't seem very likely that you will be able to convert Mario Kart Collision Files directly to Wii Game Data Files (.kcl to .szs conversion). 

It might, at best, be possible to modify both of these files using tools, such as SZS Modifier or similar.

Simply put, it is impossible to convert KCL to SZS directly.
Thus, there is no so-called kcl to szs converter or a free online .kcl to .szs converter to be found.