Heidelberg has recently published their own color atlas titled: "Process Colour Look Up Guide" - and it fills a much needed void.
Now, color atlases have been around for quite some time (see my post HERE) however their useability has suffered in many ways due to a lack of adherence to any effective print specification. Heidelberg has solved that problem by producing their atlas according to ISO 12647-2 Amd. 1:2007 printed, in the UK, on both coated and uncoated paper. That should mean that the color atlas would be valid to specify screen tint builds at any printshop that prints according to the specification.
I strongly suggest you contact your Heidelberg representative and try to secure a copy for yourself - they will likely go quickly.