The right place for the method is Lib, because its a general purpose method that is going to be used in differents places with differents objectives.
CakePHP's core has many examples of this approach like: CakeTime, CakeNumber and others.
Others examples could be seen in some of CakeDC plugins too.
IMHO @yossi was right about "assuming the data as static", but his approach of storing the data in Session just would make my code more confusing.
In my particular case I'm taking the Lib way. Thanks for the help.