So far, this is the best comic reader I've come across on linux, but I wanted to take a look at the source and possibly add some features but I can't seem to find it anywhere. Is it available?
Yes, it is. Since the program is written in Python, the executable files are the source code. All files that end in *.py are text files with Python source code, you can simply open them in any text editor.
There is a completely rewritten version of Comix (version 4) almost finished though, and I recommend you to look at that version instead of the old 3.X version, since the quality of the code in the older versions is very bad. Nearly everything is implemented in the new version, so it should work fine for you. To download it from the SVN repository, run this from the command-line:
svn co https://comix.svn.sourceforge.net/svnroot/comix/trunk comix
doy, thanks very much, I guess I figured only the installer was written in python. I'll take a look at v4.