As we all know now, R75.40 is released, and as part of it GAiA is now out. Do you want to have some pieces of its source code? If yes, you may want to look into License.txt file on the installation DVD.
This document mentions parts of SecurePlatform and GAiA to be subjects of GNU GPL, GNU LGPL and BSD license.
That means one can request source code, and Check Point has to provide it.
Well, you will not get any source code for security products, but some OS pieces might be interesting as well. In particular, dynamic routing binaries, VRRP related files, etc. If so, check the license file I have mentioned and feel free to email your requests to email@example.com.