No but if you find out, I've been looking too. I asked my dealer and they didn't have one. I have a machine shop and I thought of making a locking enclosure that went over the current plastic cap. I've already had to purchase a replacement cap as mine was missing one day at the farm. I didn't start the tractor until I checked the fuel to see if someone had poured water or something else into tank. fortunately not.
I'm serious about trying to make something. I actually have a 14,000 sq foot shop full of machine and fabrication tools that is looking for things to design and build. I bought it out of bankruptcy last year. In addition to accessories , I've been working on some speciality implements. Let me know if you have any ideas.