From the flyers they had posted I believe it's an annual event down there.
The State Department also had a sale Saturday and Sunday, which also goes on this weekend . Mostly a book sale, but also stamps and coins, hats, musical instruments, and doo-dads that various state dept peeps have brought home. Even had some sports cards. Besides though, most stuff was international. And paper money, too. I know when I left Saturday they said they were continually bringing more books out to restock. Not sure about the other stuff. This Sunday is 1/2 price day, IIRC.
There was a whole bookshelf full of Henry Kissinger's books released from the Nixon Presidential Library. I also found a 2-book boxed set that I passed on. It was a National Geographic type from the country of Palau, which had a hand written letter from Palau's President addressed to "Madame Secretary" Hilary Clinton.
The state Dept sale is also an annual event.