There are several types of Honda locking gas caps, plus you don't atually say you have a Honda 750 let alone a SOHC model.
Anyway, first thing to try is using a small screwdriver or any old key to turn the gas cap lock. Older models just have a simple catch, not actually a lock. Anything that fits in the keyhole on this type can unlatch the gas cap.
Newer models (and many other non-Honda 750cc bikes) do use a real lock. Any locksmith can open this lock and should be able to either make a key to fit, reset the lock to fit your existing ignition key, or remove the "guts" and make it a simple latch.
