Actually, try the smaller hardware stores (TrueValue, Ace, Aubechons, et al), they have a better selection of this kind of thing that the big boxes. Look in the bins where you can buy the strange stuff, like small springs, one (1) washer, nylon spacers, hex and torx keys, that kind of thing. Around here, I pay 50 cents for a 3 pack of 1/2 inch split rings, IIRC, and they are in the green section of the drawers (you'll understand when you see them, if you have the same vendor in your area). And they are heavy duty, steel split rings, I use them on my flash drives and for single keys.

Great stuff in those bins. Be careful when you browse, or you might have a lot more than you thought you would when you walk out. :P