Many Linux distributions ship a version of Bluefish or make it available through their package systems. For example, Bluefish is available through the Debian apt-system and FreeBSD's ports. You may check if Bluefish is available through your favorite software installer.
However, the main source is the Bluefish website, where the software and a few contributions are available. The download page is reachable at http://bluefish.openoffice.nl/download.html. Here, you may download the source code and binary packages for Debian, Red Hat/Fedora, and Mandrake.