When I asked the young kid behind the counter at my AAP many moons ago, I got a canned answer: "We make all our own stuff." ("Stuff" being the operative word here.)
Really? AAP makes their own filters? Lubes? Brake cleaner? Carb cleaner? Hair spray? Toilet paper? Incents? ... Come on, now; are they that hard-up for hired help?
I have a suspicion that it might be handled similar to the Wal-Mart products, using the nearest least-cost bidder? But I have absolutely zero proof at this point to back it up. Wal-mart is national, however AAP is only regional (mostly a East coast / Midwest operation with little to nothing out west). I don't know if AAP has a sister operation that would enlarge the product purchasing power.