Depending on how much legwork you want to do, you can always get keys for any lock.
Is there an alphanumeric code stamped on the lock? If so, the manufacturer will probably be able to cut new keys for you. I think many recent Sears boxes were made by Waterloo.
If there's no lock code, then the solution is probably to remove the lock and have a smith make keys for it. This may involve picking the lock, which is probably pretty easy. The smith might (1) measure the pins and cut a correct key for it, (2) grab a new key and repin your lock for the key, or (3) sell you a whole new lock that's dimensionally identical.