Rob Gronovius:
Once upon a time, paint selection was limited and modelers needed to mix various colors to get the shade or hue they needed. Tamiya still provides mixing ratios albeit specifically for their own line of paints in their instructions.
Maybe paint mixing is a lost art, but I wouldn't let the lack of a certain color stop me from building a kit. I'd use trial and error and mix up a close approximation.
I couldn't agree more! I mix probably 70% of my own colors for any given "correct" color.