Anyone know where I could find a rear lens cap for the stock 16x Fujinon lens? I've tried searching this forum, the JVC and the Fujinon sites, with no luck. I have the lens mount cover that fits over the camera sensor, but nothing to put on the back of the lens when detached.

Does such a thing exist?

Sure does. It would have shipped on the lens in the lens box, unless of course you bought yours used or already assembled.

Got mine used and already assembled. No cap. Anyone got a part number? Should I be pestering Fujinon or JVC about ordering the part?

just go to your local photography store and try a couple of sizes on. these things are standard sizes for lenses, so as long as the diameter of the cap fits you can use it.