Most auto parts stores do not carry AC Delco batteries. Stores such O'Reilly's and NAPA typically sell their own store brand batteries. AC Delco batteries are sold at GM dealerships, AC Delco Authorized Service centers, some independent repair shops or online through sites like eBay.com or Amazon.com.
A quick way to find local AC Delco parts retailers is to use the AC Delco store locator function on the official company website, ACDelco.com. This does not return results for independent auto repair shops that stock and sell AC Delco Batteries, nor for GM dealership parts departments. It does show authorized AC Delco Service Centers, which are part of a nationwide network of affiliated service centers selling and stocking AC Delco parts, including batteries.