If the problem is a broken lock cam, it can be replaced. If the issue is a broken transfer mechanism, then you may be SOL if you can't make your own parts. You'll have to remove the top few drawers and inspect the whole assembly to determine which parts of the locking assembly are affected.
If it is the lock cam, then call HF customer service (don't bother to email) and see if they will send you a new lock (you may have to pay). You will need the model number of your box or the rep won't have a clue how to help you. They're "on script" and aren't really familiar with the products that the company sells. If they tell you that they can't sell you a new single lock, then you can buy a 5-lock keyed alike set that is made for the 44" box system. It should run about $35 shipped. They won't know about the lock set unless you tell them the part number and then they can look it up. The part number for the 5 lock set is HF
item #12892.
I've had better luck calling during the week. On the weekend the call was answered overseas (the Anglican name didn't match the accent) and the rep was useless.
I used it (with modifications) to key alike a HF 26" stack with a pair of side cabinets on each side, and the 5-drawer cart.
If the issue is with the locking assembly, then I'm not sure I can help. I don't own one and have never stuck my head in one to see how it works. Something may be binding, or one of the transfer parts may be broken. Check to see if the mount on the back wall has popped a weld. Could the catch on the back of one of the drawers be bent and binding the gravity bar ?
