I do believe that is one of the prettiest bikes I have seen...
I saw some of those on a site once when I was searching for gaurdian bells, you could get them with different colors in the center. I am sure you could find it if you googled long enough. Also, might be able to find something at a Lowe's or hardware store, it is a cap, and a specific size that would fit into a big allen head bolt. Here is the SKU 90312-MCH-010 for Babbits,
http://babbitts.motorsportdealers.com/pages/parts/viewbybrand/7/Kawasaki.aspx Still don't know why it always says kawasaki at the end, even when you are viewing schematics for the vtx... you can go in, choose your bike, and then click frame, it is part #13 on that list, 2 of them for $4.34, but hey, I'll sell you mine for $35...
Edit: guess I didn't really need to add the picture... its the same as my sig. line... my bad