Regarding the tank and seat locks:
I believe (at least from other models) that those accessory locks have fewer matching requirements on the key
i.e. ignition key will open all, but one made from the accessory locks will not necessarily operate the key-switch lock.
It would really be best to remove the key-switch and take that to the locksmith.
If you don't want to mess with drilling out the anti-tamper shear bolts, then just take the top triple off the forks (of course need to remove the bars) and take the yoke with key-switch attached. You pretty much have to go through those steps anyway to get access to the screws, even if you did decide to drill them out.
Gas cap - again my knowledge is based on other Triumph models - there is a hidden screw that is only accessible once you open the cap - so is not possible to remove a cap assembly that is locked, without first getting it unlocked.