Sorry to hear about losing your keys! That’s super frustrating.
You could also try to call the company that makes your toolbox. They may even have an FAQ on their site that describes how to get into a locked box that you own.
The last resort is to try to pry open the box yourself. A crowbar or other type of tool may break the lock. While you may be able to get into the box this way, you’ll likely need to purchase a new toolbox after the fact, which can set you back a pretty penny.
If you do, make copies of your key to avoid being locked out in the future.