Note: https://hpiers.obspm.fr/iers/bul/bulc/README states:
The files in this directory and sub directories are licensed under the Creative Commons Attribution 4.0 : CC BY-ND 4.0
http://creativecommons.org/licenses/by/4.0/
which means it's 100% OK for our users to download it. This is the primary source and they have beefy servers. We could distribute it with the base system even, though our users aren't allowed to distribute altered copies. I'm not putting this in the base system, just a pointer.