Try Marks' Standard Handbook for Mechanical Engineers or Machinery's Handbook.
If you don't have Marks' or the Machinery's Handbook available but you have an iPhone or iPad, there is an app for that from Martin Sprocket and Gear:
Not sure if there is an equivalent for Droid.
Machinst Handbook is no help with it comes to C.P gears. I just checked out that martiansprockets.com and I didn't see anything that was realted to Circular Pitch gears.
According to my old copy of Mechanical Engineering Design by Shigley, circular pitch is just a different way of specifying the pitch. The normal pitch, P=N/D, where N is the number of teeth and D is the pitch diameter. Circular pitch, p=pi*D/N. Thus p*P=pi. So you should be able to use your normal equations, calculating your value of P from P=pi/p.