Somebody knows... Maybe you?
I have an old NCR and needed keys, bought a complete set for all doors ages ago. I think I had one or two spare keys, but can’t remember which ones and would need to check. I think all the keys are the same across the models, but not an expert of course.
Mechanically done. Just needs the glass when it's ready and a layer of finish on the wood once it warms up. It deals out the Kit-Kats perfectly now after a little extra grinding in the corners on the slide.
I had a look for National keys and the only duplicates I have are number 1 and 2......I believe if the key you are after was like the picture you shared, it would be a number 5 not 406. The 406 maybe associated with the model of machine.
At the moment none on U.K. eBay, but loads in US.....there a sets for around $25 plus shipping....