If you lose the keys of your toolbox, you can contact the manufacturer of your toolbox to see if you can order replacement keys. Larger toolbox manufacturers usually have replacement keys that you can order, and the prices vary.
To order the right keys for your toolbox, provide the manufacturer with the number on the toolbox. Alternatively, you may get a replacement key for your toolbox from some online key cutting services. As of November 2015, several sellers on eBay offer this type of service for Craftsman toolboxes. Provide the seller with the number on your Craftsman toolbox to get the replacement key for the box.