There is a whole archive on the Surly site with old models and paint codes. A bit of Googling should find it.
EDIT: seems to have been turned into an email instead
What is the RAL color code for my frame?
RAL is a color code number system used by paint manufacturers. We can provide this code for most but not all of our colors. You can contact us at Derby@Surlybikes.com. Please provide the model of your Surly, its color, and the frame's serial number to aid us in your quest.