The terms of the GFDL require certain access to source text. Any element of the GFDL text corpus must remain available in source form to anyone, and no page in it can be distributed without the URL of a source form that can be instantly retrieved by anyone. This includes those "banned" by the sysop power structure. Mediawiki provides this with "edit page" or "view source" links on every page, and the Special:Export facility in recent versions.
Some individual wikis may provide bulk releases in various formats as well, as we do. See MySQL dump for instructions on downloading.