Widgets and samples for ArcGIS Viewer for Flex are now accessed directly from ArcGIS Online.
This and other resources for working with the Flex Viewer are also accessible from the updated http://resources.arcgis.com site at http://resources.arcgis.com/en/communities/flex-viewer/.
You will be automatically redirected to the Flex Viewer content on ArcGIS Online. Please update any bookmarks.