I'm writing a text where I discuss where our modern democracy has its roots, and when writing about Athenian democracy I figured I needed to find out the dates on when the sources of the Athenian democracy was found. But I can't find anything that is "early enough" to be considered an inspiration to our modern democracy. So basically I'm looking for the first sources that say something about how Athens was ruled.
So you are looking for a constitution of the Athenians? Try Aristotle's or Pseudo-Xenophon's. They are the two simplest primary sources that give a good overview of how Classical democracy worked.
I'm sorry if I am not more helpful but I'm not too sure if I understand what you are asking.