A couple houses ago I ran into the bazaar issue of snapping a mailbox key in the cluster mailbox for a house rental we were in. Never running across this before, as a typical moron my first thought is I have to go to the post office.
Sidenote: Under an usual circumstance, we had 2 residences for a few months and let me tell you, I do not recommend having 2 residences for many reason, however near the top of the list would be managing your mail. You, as an entity in the US cannot have 2 addresses. You can forward your mail for a particular amount of time, or put in multiple address change requests, but all kind of shaky. USPS delivers a lot of our packages these days, even from Amazon. We wound up losing a couple things, probably due to porch pirates - one in particular was a box I saw delivered on my security camera, but when we got back to that residence, it was gone. It was an apartment complex and the office knew nothing.
Sidenote cont.: In this process we went to the Post Office on Elliot and Val Vista in Gilbert, Arizona and they were unreasonably nice to us. A manager came out and gave us a direct phone number to ask questions during our transitions. Amazon service, I hope the USPS keeps that up. Okay, end of sidenote.
I went to the Post Office (not the one in the sidenote) and talked to them. They said that they would be able to change out the lock and get us new keys and there was no fee for that! Yay! However, the process requires the post office to put in a 30 day hold where we'd have to go to the post office to get our mail all of the time. My wife checks for packages frequently so we'd be driving and waiting in line at the post office almost every day!? Pass.

The post office suggested we ask the HOA to see if they handle changing the lock before we submit the request and have our mail taken away. I know that sounds dramatic, but it did seem stressful. I reached out to the HOA and told them what happened, they said they do not handle the cluster mailboxes and that I need to go to the USPS.
Fine. So then I begrudgingly go back to the post office and submit the request and they can hold our mail. But today, there was a $40 fee to get that lock changed. I protested but the other day there was no fee! "Who told you that?" - "I don't know, I don't work here!". So I fumed for a minute while the line of 20 people behind me also fumed. I tried to pay the $40 fee but my credit card wasn't working. Wasn't me this time! Our post office has had issues with their readers so I think it was that - or was it karma?
Never got to start the process, but went home still fuming that it's $40. It's a key and lock - can't be that much. Called the rental company to see if I do pay this $40 can I get it reimbursed. Not my house, right? Nope. I contemplated just continuing to use needle nose pliers to get the mail everyday. I mean, it was working fine. My mailbox today is just a regular mailbox that doesn't even lock - what's the difference?
Then I had a though, if the post office was saying I could get the HOA to change the lock - can anyone? And the point of this blog post is that yes you can! Why would USPS care, they don't use those keys, they use a master key that opens the whole cluster! It all makes sense now! I went to Amazon and found numerous key/lock combinations. Due to the shape of the key and lock and narrowed it down to two.
This first one was cheap:
Prime-Line Mailbox Lock, ILCO 1003M Keyway, Nickel, 90° Rotationhttps://www.amazon.com/dp/B000B4N0PCI hoped this one would work and it did! $10 was way easier for me to spend on a lock than $40, not to mention the runaround. It was very easy to swap out the lock and it came with different installation mechanisms for other boxes.
Turns out the second one is no longer available; I also see there's the same lock where you can get 2 for the same price so I'd do that if you have 2 mailboxes you need to fix?