There seems to be a run on HC-110 developer, and it's out of stock all over the place. Indeed, if you start typing "Kodak HC-110…" in a Google search you'll find "Kodak HC-110 discontinued" as one of the common search terms.
This developer is used with most of the B&W films, including many T-Max and Tri-X versions, so it would be big news if it was discontinued.
What seems to be the case is that it is no longer produced in the US, and no longer in 16 ounce bottles. New bottles are 1 liter only, and made in Germany.