It looks like the zero is dead! Adafruit no longer lists it as an active product only the new zero-w, which is (as was the zero for most of its life), out of stock although I managed to snag two on the rare times they were in stock. I guess they found that $5 wasn't a supportable price point, too bad ...
(edit) spoke too soon, the Canadian distributor appears to still have zeros (although limited to 1 per customer) at $5, perhaps only adafruit has dropped them.
Peter