I have created a project on Google Code where the source code for the gadgets is available. The Google Code project also hosts the download files of the gadgets.
To download the source code for a particular gadget just visit DesktopGadgets on Google Code. The code is in the subversion repository which can be accessed by any subversion client.
The source code for the gadgets is available under the Apache 2.0 license. If you build any derivates please let me know so I can check them out ;)