Alex - it's in the William Optics section of the website, bottom of the page, first section of the lists rather than pics bit... under spotting scopes.
http://www.andrewscom.com.au/site-section-10.htm
Not a bad price - certainly much cheaper than in the UK but WO will sell them direct for US$400 for the cell only or about US$440 for the cell, extension and 10:1 focus upgrade
Arthur