At the moment, it is nearly impossible to find a COVID-19 test. With millions preparing to travel to spend the Christmas holiday with their family, Americans are descending on drug stores en masse and treating at-home COVID tests like hickory honey hams. President Biden announced that at some point in January the government will set up a website that allows you to get the tests delivered free to your door, though the details of this operation remain murky.
Assuming you have not been able to locate a COVID-19 rapid test at your local CVS or Walgreens (both of which have restricted the number of tests you can buy in a largely unsuccessful attempt to combat hoarding), your best bet is to buy one online. Unfortunately Christmas is a few days away and tomorrow is the biggest travel day of the year, so this is not going to do you much good before your flight. Still, with the Omicron situation constantly changing, it is smart to load up while you can.