Hi Wim…………….
I have no idea, but was thinking. Is the fuel cap key the same as the ignition key ? If so can you see the number on the ignition barrel and get a key cut to fit. ? How about the tool box ? Is there a barrel number there ? Honda still do keys, I know because I tried to get a blank everywhere and they were only available from honda. I got a spare one for my RD ignition switch.
Again , I have not seen the underside of a CB fuel cap, but that may have a part number on it ( for the key ). My RD did not have a locking fuel cap. Guess you could remove yours and go for a non locking cap if it would fit. Consider draining tank and taking it off and taking the whole thing to a locksmith who should be able to open it easily. Then look for the lock number &/ or take a blank key and ask if they can cut you a new key. I’m fairly sure you can change the barrel part of the locks or perhaps one from a CB900 F may fit .
I am not sure I would want to drill the lock with a tank full of fuel vapour…………..just takes 1 spark and potential very loud bang .
I am sure you have thought of most of this , was just thinking aloud and think many options are worth exploring before butchering an original lock.
Regards,
Nat.