Create an account at Avid.com and Register your PT9.
Within your Avid account will be a "My Products" link - follow that and under PT9 you'll be able to open up a 'downloads' section, within there will be a full 9.0.5 installer you can download.
--note from Avid: Software installers are only added to Your Products in an avid.com account if you purchase+activate software online, not if you register a boxed copy.