I hate to see all the back and forth drama here, and it's a shame it came to that, but I'll throw in my own two cents, while pretending like that crap didn't happen....
Ever hear of "Heinlein's Razor"? It's a statement that says...
"Never attribute to malice that which can be adequately explained by stupidity, but don't rule out malice."
In my experience, any sufficiently large organization, including things like the post office, is going to be chock-full of incompetent morons. Considering all of the very expensive, easy to identify things that get shipped every day, I would be pretty surprised if someone outright stole a box full of sheaths with intentions of re-selling them
Now, that's not to say there definitely wasn't greed involved - they could have fallen off a truck, or gotten delivered to the wrong address, and been kept, or someone could very well have outright stolen them. But in my experience with ANY package delivery service, it's far more likely that they are sitting in a warehouse or office somewhere waiting for someone with a clue to figure out that they aren't supposed to be there.
Here's hoping that is the case and your sheaths are simply lost, and get returned soon. No matter how it happens, it sucks that the package went missing and I wish you the best in the whole situation.