some big brands actively don’t supply paint, even if you ask for it, to prevent counterfeiting.
I’ve not heard that one. The way I had it explained to me was that most wet paint frames are a combination of a base coat and a laquer, and it would require a whole seperate paint operation to create a paint match for a single pot application, which in reality can be colour matched from a model shop.
I suppose if I ever did bikes again, I might start with a known airfix colour then reverse engineer the frame colour from it. But I’m not so I won’t.