Plenty of eggnog mix is sold in the US, mainly between about November 15 and New Year's. However, it is my perception that it has become less popular in recent years, at least in the circles in which we move. We don't attend many pre-Christmas parties, let alone the many business-related events I used to attend. I can remember many occasions in which an eggnog was available, although there were usually some alcoholic as well as non-alcoholic alternatives.
I can remember making eggnog from scratch, but in recent years we have relied on commercial eggnog mix. We have several family members who will have one eggnog when it's available, but one of our sons would find the holidays incomplete without it.
My recipe is straightforward: 10% brandy, 10% dark rum, 80% eggnog mix, with grated nutmeg sprinkled on top.
We were given most of a "leftover" half-pint carton of "light" eggnog mix on December 27, so I made a weaker-than usual serving daily. I finished the last of the mix on January 4. No more until next Thanksgiving, I imagine.