I strongly recommend paintscratch.com, from personal experience.
I had them mix a paint stick of of Magenta for my TR6 from the paint code and it is a very good match, almost perfect. I also had them mix a paint stick and spray can to match the non-standard color of my airplane from a small fairing that I sent them. Again, I was very happy with the result. Also, the person I talked to at Paintscrath was very knowledgeable about paint, compatibility, etc.
w&w