If the mounting tubes are flat it would be fairly easy to retro fit a generic set of flat side bars. You will probably have to do some chop cut reweld to the new side rails but you’ll be working in 2 dimensions. If one or both of the mounting tubes angle up it will be near impossible to bend someone elses side bars to fit. In that case I would cut them off the frame and re-weld them flat to match up to something that’s commonly available.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience