I had good luck just using Google to search out my city's code. I live in Chicago so my search words were:
Chicago municipal code
Worked like a charm.
The actual location of in the municipal code may be kind of tricky. SeaChick's suggestion to search within the code for certain terms is your best option.
Thank goodness Chicago allows chickens, and even has no limitations on number. I'm only planning on getting 3 hens, and have alerted the nearby neighbors so I don't think I'll have any problems.
Interestingly, it is illegal to raise pigeons in a residential zone in Chicago. Guess there were a few pigeon fanciers who ticked off their neighbors...