Each G-20 meeting has created its own Web site of documents, with varying degrees of comprehensiveness. No central repository exists of G-20 documentation, but some recent initiatives might help.
Bloomberg Law has started a G-20 Declarations library under the “Global Law” tab. It includes declarations from the G-20 summits since 2008.
Search > Global Law > World Organizations > Group of 20 > Declarations
An open access repository is being created at Archive-It. In addition to final proclamations, it should include preliminary documents and reports from experts and working groups.