I have two practically new Kawasaki Ergo seats that fit the Z400 or the Ninja 400. Used once or twice, no marks, tears or anything. $200 each, shipped. Info from the Kawasaki web site:

Item # 99994-1041
Made to tailor fit and complement the Z400 or Ninja 400 motorcycle, this seat enhances riding comfort for taller riders.
The ERGO-FIT® extended reach seat is 25 mm (1”) taller than stock and comes fully assembled.