Bagger John - I'll post this information here for posterity. I'll shoot you a PM about the extra bracket I have.
Corbin actually posts the installation instructions for their seats in a tab called "Notes". For the modular seats you can see the installation instructions here:
https://www.corbin.com/kawasaki/install_k-c8-f-e.pdfIn the instructions it has a parts list. The bracket is listed as:
#A00947 Corbin seat bracket
There are pictures in the installation instructions of what the bracket looks like. Basically a 10" metal bar with a pointed nipple in the middle that gets screwed down on the two ends.
I called Corbin and got a very nice young lady on the phone that went out of her way to help. I gave her the part number and she said, "Ok, let me go out and speak to the warehouse manager and make sure we have one." They sold it to me for $45 plus $5 shipping. I'm not sure if they would always do that or if they would tell you to pound sand? Might be a matter of who picks up the phone.