Accessing the 4chan deleted archive is not straightforward, as it is not officially available through the site itself. Unofficial archives and databases have been created by enthusiasts and researchers, but these can be ephemeral and may not always be accessible. There are some public torrent files available containing 4chan's /pol/ board posts from 2013-2018.
The Digital Dust: Exploring the Lifecycle and Legacy of 4chan's Deleted Archives 4chan deleted archive