I personally haven't noticed any currently being reproduced, but that's not to say one of the usual repro stores like Z1 Inc. aren't thinking about it. I would email them and inquire about the possibility of them reproducing those pans, which will fit 73-76 H1/KH 500's.
Otherwise, your current ebay choices for used seat is this from a fellow board member
http://www.ebay.com/itm/Kawasaki-H1-500-KH-triple-original-SEAT-NEVER-RECOVERED-/221403265904, which is a heck of a better deal than this one
http://www.ebay.com/itm/Kawasaki-H1-Triple-500-Mach-III-Used-Original-Seat-Base-Assembly-1973-IBK-/400684996456.