I usually just go to the nail polish aisle at WalMart. Sometimes works well, sometimes not so well. Colors can look right in the bottle but be too thin to cover well or dry to a different shade.
You might look through the paint codes here and see if Iris Blue is listed:
vintagecannondale.com
You can have an automotive paint dealer scan your color and try to match it. This is expensive and hit and miss. Friend had it done to match paint on his Harley Davidson and the color was way off.