I cannot speak for any area other than right here in the Richmond VA area but both located around me have a separate pull out drawer and it is actually labelled "gun screws". ACE Hardware stores, at least these two, are franchises so the owners are completely different, so is the staff, some know what they have, other don't.
The biggest problem is that YOU have to know what you want exactly in terms of thread (dia and pitch), length, type head flat slotted, dome, round head etc.
I do NOT advise taking the gun into the store, so you have a tiny screw in your hands but most all the screws in the drawer will look "pretty close" so again know what you want and chances are ACE has it, already blued and ready to go. One of the stores even has a labelled piece of metal with threaded holes so you can "try" your screw for fit and ID, but be aware, little screws inserted by your fingers in a loose piece of metal (or plastic) may "feel fine" but in reality may not be correct when you go to tighten in the gun.
Anyway...just a shot and again, some ACE Hardwares are very much anti-gun I've heard and won't even stock these drawers as a couple of my friends in other states have told me.
Hmm, I haven't tried any of those screws for things such as side plates. Most of them to me seemed to be for scope mounts etc. I may have to look closer.
Rosewood