If you are curious about how to do this yourself, I recently made a video tutorial on how to get boundaries that are not included by default in CODAP onto maps in CODAP: https://www.youtube.com/watch?v=3VHTb9giboE
Another thing that is not in this video is you can create your own GeoJSON file if you can’t find a pre-existing one you want by searching online, drawing your own custom boundaries, and then importing that GeoJSON file into CODAP. Here is a site I used with guidance that helped me create my own GeoJSON boundaries for two small islands off the coast of Maine that I then imported into CODAP: https://support.planet.com/hc/en-us/articles/360016337117-Creating-a-GeoJSON-file