Since cl-gdata is currently under development, anyone who is interested in looking at it has to download it from the source repository. The code is available on Google Code.
To download the latest version of the source, simply run the following command:
hg clone https://code.google.com/p/cl-gdata/
To load the package and all its dependencies, the easiest way is to make sure you have Quicklisp set up, then add the path to cl-gdata to the ASDF *central-registry* like this:
(push #p"/path/to/cl-gdata/" asdf:*central-registry*)
And then simply load the package using Quicklisp: