Thank you, my search was clearly too hasty, I was just getting US results and when Amazon didn't sell them, I assumed it wasn't a thing here!
Cheers again.
Rather than messing about with keys that might get lost, it struck me that a combination lock for the draw and door of my desk in my home office, might be a solution for securing it (pictured).
Some searching has revealed that there doesn't seem to be a ready made solution for this...