The source code for the FSBL is included with SDK. Create a new C application project with a standalone OS, then select FSBL from the list of template projects.
SDK is part of the ISE Tool Suite from Xilinx, you should have a copy with the Zedboard (which will be much quicker than downloading it). A WebPACK license will support Zynq development for free.
ISE is not open source, but you can download it (for free) from the link I gave in the last post. If you're going to develop for the Zedboard it is definitely recommended that you use Xilinx's tools.
That gives you PetaLinux, what you want is "Vivado and ISE Design Suites - 2012.4 Full Product Installation". Choose the installer for Windows or Linux depending on what OS you're running. After that I'd recommend following the "Zynq Concepts, Tools, and Techniques on ZedBoard" guide from this link:
