Do you mean the example from the Telerik Controls Examples app in the Store (see attached screenshot)? If yes, you can find the source code in the examples that ship with RadControls installation.
When you installed RadControls, if you had chosen to install the examples as well, you got them in ~\Program Files (x86)\Telerik\RadControls for Windows 8 HTML Q3 2013\Demos
The example that you are looking for is placed in ~\Program Files (x86)\Telerik\RadControls for Windows 8 HTML Q3 2013\Demos\examples\Grid\FirstLook but to run it, you need to open the entire QSF solution.
If you did not install the demos along with the controls, you can uninstall RadControls and install them again, making sure that you have the demos checked in the installer.
Let us know if you need further help with accessing the example.