Seems if you're looking to replace individual Craftsman pieces, even though the store may not carry singles they should be able to order them. How else can they make good on the lifetime guarantees for sockets? If they won't do it, an Orchard Supply Hardware has single Craftsman pieces including sockets and wrenches.
As for the workaround fix for your parents, if you've got a bank account, your bank should be able to hook you up with an ATM / Mastercard that draws off the account just like writing a check. OR failing that, how bout a PayPal account? Works good for a lot of vendors including the Bay. Whaddya think? ;>)
Mark