You can download our modified open source GRUB2 and grubinst code here:

http://www.vmlite.com/index.php/download/vboot/49-grub-1-97beta4-and-grubinst-open-source/download

VirtualBox source code that VBoot have used is the unmodified version of the virtual disk source in version 3.2.6, that you can download from this location:

 http://download.virtualbox.org/virtualbox/3.2.0/VirtualBox-3.2.0-OSE.tar.bz2