I suppose finding used 2016 Ninja 300 abs krt where someone crashed left side and parting out right side panels may be difficult.
Check out racing forums & Facebook groups. They often replace factory bodywork with lighter tougher fibreglass/CF versions. So there's leftover OEM bodywork lurking in back of garages.
How about this?
https://www.amazon.com/dp/B07DJZ8HVC