I was thinking about this and may go the long way around to complete one.
I have some old Size 10 Allen keys in the shed, if I cut them down to size then its a case of grinding, filing them down to the correct shape and engraving the end with a Dremel.
Probably various (very) easier ways of doing it, but thats my starter for now. The metal matches and I could just blacken it a number of times by heating and treating with Beeswax for that nice black finish