I asked at the dealer, and they don't have a locking gas cap as an OEM accessory. Is there a recommended one that has maximum likelihood of compatibility with a 2013 Fit?
As for how to install it, my current plan is to ask the dealer (which has a shop) if they would do it. Failing that, their is a private shop that I will turn to.
The suggested option should be orderable from Canada. If it has a tether, so much the better, but that's secondary.