To find more newspaper articles about the Yirrkala Bark Petitions you can go to the website of Trove, at the National Library of Australia. Click on “Digitised Newspapers and More” and enter your search terms.
http://trove.nla.gov.au/

The Indigenous Rights site, hosted by the National Museum of Australia, also contains digitised newspaper articles
http://www.indigenousrights.net.au/subsection.asp?ssID=83&1=1#iID911