Salt Cloud is now part of Salt proper. It was merged in as of Salt version 2014.1.0.
Salt Cloud depends on apache-libcloud. Libcloud can be installed via pip with pip install apache-libcloud.
Installing Salt for development enables Salt Cloud development as well, just make sure apache-libcloud is installed as per above paragraph.
See these instructions: Installing Salt for development.
Current Salt release: 2014.1.6
Docs for previous releases on salt.rtfd.org.