Nige,
Your question about paint codes prompted me to look around and I found this website that is an amazing resource ... check it out. The company is Paintref.com and their name says it all.
PaintRef.com - Automotive Truck Fleet Paint Color Code Cross Reference
I know your project is just getting started and you have a long way to go, before you choose a color. For my build, selecting the color was one of the most difficult decisions to make. Even if you narrow it down to Red or Green or Blue, there are so many shades, with and without metal flake ... trying to match a historic car or coming up with something of your own. Lots to think about, but then again that's half the fun!
- Tim