Home Depot Key Copy Service. If you paid by check they should be able to find it using your account info. For a metal key, it takes no more than around 5 or so minutes, and just $1.50 for each key copy.
However, there's a limit to the type of keys the good people at home depot can copy. The customer service associate did note they cannot cut a laser cut key, which is a key with a smooth side and the center bored out, or a switchblade key, the store will not be able to copy these keys for you. Getting keys copied is simple, and can be done at home depot!
Just take the debit/credit card you used and request a copy of the receipt.
Depending on grooves and the specifications of the key that you have, home depot might not be able to go through with making an accurate enough copy. You’ll only pay the price of the key and nothing more for the service. Although, you need to bear in mind the design of the metal key that you need. Home depot does have a limited selection of transponder chip keys that can be cloned at some home depot locations.