I want to download packages for years 2000, 2001, 2002, 2003 and 2004 but Debian snapshots are maintained from March 2005 only. How can I get the source of packages before 2005?
You can find old releases of Debian here. You won't find all the snapshots of packages, only the versions that were released.
You can find cd images at archive.org. https://archive.org/search.php?query=creator%3A%22Debian+Project%22