For some selected groups of satellites, Celestrak has already-built group definitions of satellite archives at https://www.celestrak.com/NORAD/elements/
Another option is to subscribe to Space-Track.org. You have to register using your name and e-mail address, then verify, but it is a straightforward process. Make sure to read all of the instructions and rules first.
Read the USER AGREEMENT first!
Then at least browse everything else.
You can read more about using Space-Track in this answer
One you are registered and logged in, select
TLE search from the top menu:
Then enter the satellite number (21639 for example) and click all of the options shown below, and you will get all of the TLEs so far for March, 2018.
If you click the blue
API button, it will build a URL for you and then open it in a new tab. You can save that URL and alter it or rebuild it later with Python.
You can also save the data in the new tab directly from File->Save on your browser.
Read the instructions in more depth if you want to try to do this automatically from a script. Visit
HowTo from the
Help menu: https://www.space-track.org/documentation#/howto
Remember you need to use your personal log-in before you can access the site, even using a script, and remember to
Follow All Rules