A few thoughts come to mind.
I am not aware of a two part boot for the drive shaft coupler boot. They are all one piece for Kawasaki's.
a: Call Jim Sether at Taylors Kawasaki (Woodburn OR) and see if he can locate one via Lightspeed. Their number (503) 981-1813. I'm in Eugene and he has done a great job over the years at assisting me in locating NOS parts for my old KZ's.
b: #2 would be to watch for the next teardown on eBay, or maybe a member of our fine forum may have one.
c: Do a national Craigslist search via
www.searchtempest.com and look for ZN parts.
It looks like 49006-1020 fits all 1300's in the entire family of bikes.
Best of luck.
Todd.