Herschel is not ready yet. It's not even working as a real compiler yet. If you are interested in it anyway, you can get it's current source code from the public mercurial repository at bitbucket.org either by snapshot or by mercurial clone. For the later run this command from in your terminal:
hg clone https://bitbucket.org/hvellyr/herschel
To get a snapshort of the tip of the latest development (not necessarily the master branch) click here.
More info, including source statistics, etc. can be found on ohloh.net.