1. Check with your local PD. Project ChildSafe from the NSSF makes free locks available to PD's. Often they sit in a closet. Ask for some.
2. ATF regs/Federal law says the dealer must "provide". That means the lock or safe storage device can be sold or given for free.
3. It doesn't mean the customer must walk out the door with it. Often I have customers pull that crappy lock out of the box and give it to me.
4. The plastic box if lockable, is a secure storage device.
5. So are guns with an integrated lock (hello S&W)
(34)The term “secure gun storage or safety device” means—
(A)a device that, when installed on a firearm, is designed to prevent the firearm from being operated without first deactivating the device;
(B)a device incorporated into the design of the firearm that is designed to prevent the operation of the firearm by anyone not having access to the device; or
(C)a safe, gun safe, gun case, lock box, or other device that is designed to be or can be used to store a firearm and that is designed to be unlocked only by means of a key, a combination, or other similar means.