I think this is 1.4, but you were not entirely specific, a good place to start:
http://svnview.digium.com/svn/asterisk/ ... xt%2Fplain
Also, linux allows for the installation of the the source code (and compiling from same) on virtually all software on every distribution. Asterisk is available for most distros (Ubuntu, Gentoo, CentOS included directly from within the OS). Failing that, it can easily be downloaded from Digium's site by entering a download command at the CLI in linux or by clicking to the right spot with your I.E. or Firefox browser (the entire program, any version, all source code as a compressed file ready to decompress and compile or decompress and browse at your leisure on your laptop).