SeaBIOS may be distributed under the terms of the GNU LGPLv3 license. Both source code and binaries are available.
The SeaBIOS project uses the git revision control system. To download the latest source from revision control, run:
$ git clone git://git.seabios.org/seabios.git seabios
$ cd seabios
There's also a website to browse the latest source code online.
Released versions of the source code are available at:
http://code.coreboot.org/p/seabios/downloads/
Please see releases for information on each release.