For a aftermarket rear fender for the Kawasaki Vulcan 900 Custom you very likely have to look overseas. Online shops, like Bikebandit, sell some fenders and mud-flaps that can be used with a Vulcan 900 Custom.
If you're not a mechanical / technical person it's maybe best you search online for a Kawasaki Vulcan 900 Custom specific fender as from experience a “universal” rear fender for a Vulcan 900 takes some work before it can be fitted.
Meancycles has some bolt-on rear fenders for the Kawasaki VN900, but with US$ 262 they not cheap...
I have just bought a 2016 Kawasaki Vulcan 900 Custom but would like to change out the rear fender (Mud Guard) which looks like it is from a dirt bike.
Any info where I could buy a new one with a lower profile to the tyre would be much appreciated.
Thanks
Johnjh