Below is a link to a ZIP file that contains all the source code and assets for the Flex 4.5 examples that are used in the core documentation. This includes the *.mxml and *.as files, as well as the stylesheets, images, videos, audio files, and other assets that they use. This ZIP file also includes the mobile examples. It does not include the compiled SWF files for these examples, but it should be useful to you if you like to search for and look at source code for the Flex 4.5 examples.
The ZIP file is organized roughly by topic. For example, the Spark DataGrid examples are in the code\dpcontrols\sparkdpcontrols\ directory of the ZIP file. The mobile skinning examples are in code\mobile_skins.