I'm not sure if I can mention the supplier or not but I' will say that he manufactures high end single shot rifle actions along with other firearm related products.
Why not mention this checkering cutter supplier? We have guys who advertise their businesses every time they post via links or their tagline. If I had to guess, I'd guess you are talking about either Martin Hagn or Glenn Sokora. I'd lean toward Martin Hagn since he manufactures more than just high end single shot actions.
Now for my question... where do Europeans get their checkering cutters? I find it hard to believe that the whole world depends upon Dem Bart or Gunline checkering tools. I recall reading about someone who was producing carbide cutters in the Custom and Classic Rifle forum a few years ago, but can't recall who it was.