Wow, I would've bet a lot that an auto parts stores doesn't sell 1/4-22 hex head screws.
The local Ace Hardware actually carries some "gun" screws like 6-48 and 8-40 and a few matching taps only because they are literally around the corner from the CO School of Trades, a "Gunsmithing School."
As for finding a 1/4-22 screw at Napa. I ain't buying it. They're only used for Mauser action screws, ain't enough demand for them for a store to warrant carrying them.