You must be thinking of something else. Maybe the Mini? iPhone 13 Mini was discontinued last September.

1st generation SE had been discontinued long before the 2nd was released, but the 2nd was directly superseded by the 3rd, and you can still get the 3rd new, directly from Apple.

It's still being sold, although we are getting to the end of the two year interval in which it has gotten recent hardware updates. The last two updates occurred in early 2020 and 2022.