I've been calling many Apple certified retail locations (i.e. RadioShack, Best Buy, Target, WalMart), Apple Stores, and Sprint stores, and none of them have any iPhone 4S (unless it is 32 or 64GB, but I don't feel I need that much storage.) So I really need some help/ advice on where to buy one or when I should check. Thanks for the help!
Good luck on that. I ordered mine via the Apple Online Store when pre-sales were up. There's your best bet, if you don't mind a wait.
Try the major outlets next (Fry's and Newegg come to mind, but there are others).
Closest Sprint Store to me (on Kent East Hill, WA) was running short when I went to turn in my BB Curve for credit and bought a half-shell case for the iPhone. I suspect the shortfall is all over the place.