Glen,
Unfortunately, I am not aware of any UK sources but there are French companies who advertise on-line. Sadly, they are generally not a cheap solution and, since our divorce from Europe, many organisation are unwilling to ship to England or else charge silly money for doing so.
However, if you are in France you will find many French hardware stores with a key cutting facility often have suitable blanks.
If you are lucky enough to find an older, independent, place they may even have original Ronis items rather than later “aftermarket” blanks.
I do have a very small selection of old keys. If you are prepared to let me know your key number I shall be happy to check in case I do have one. If so, I suggest you send me the number by email to : president@traction-owners.co.uk
B…..