How can they object to "unofficial" releases of Free (tm) software when anyone can pull the code and build it.
GNU Boot seems to be Libreboot with very minor differences (mainly documentation) + removal of binary blobs.
Check https://lists.nongnu.org/archive/html/libreboot-devel/2023-0... and https://lists.nongnu.org/archive/html/libreboot-devel/2023-0... to see the patches.
There is also a Savannah repository but history does seem to have been deleted: https://git.savannah.gnu.org/cgit/gnuboot.git