Unfortunately, we probably can't sell you just a key, but we're happy to try. If you look on the face of the lock, there should be a number printed on it. Let me know what that number is and we'll see if we have any matching keys for it.
If we don't, your best option will be to have a locksmith replace the lock. The lock and key set sells for $40 and can be ordered here.
You can find the instructions to replace the lock here