RANT re: Priority Snail Mail

What's up with the box printers??? I have been to the post office TWICE for small and medium sized Priority Mail flat rate boxes. Both times they had NONE. I ordered them online from USPS.com at last, I got a shipping confirmation e-mail on Wednesday - but still no boxes. What goes on???? Thank goodness what I am shipping is not urgent or on a deadline. But geez. I can understand the document sized flats being in demand, and they had plenty of those. However, those of us who want to ship a couple of hanks of yarn are totally out of luck. Something is wrong with this picture!!!