Buying Parts in 2011

When I accidentally fried the alternator on our Cadillac,hooked up the battery up backwards really stupid beginner mistake on my part, we went to Autozone 3 times. They never had the correct alternator. We eventually went to OReilly's and they didn't have it in the computer. But one of the guys there worked in garage and and checked in the book. They had it under a different part number. So the older guy working there learned something that day, and I learned to always go to O'Reilly's if Autozone doesn't have it and talk to Kevin.