Every day, a zip is made which contains the sources as they are on this day, they are available from the FTP site:
http://ftp.freepascal.org/develop.var
This will lead to a download of the sources of the development branch:
ftp://ftp.freepascal.org/pub/fpc/snapshot/trunk/source/fpc.zip
and also of the fixes branch:
ftp://ftp.freepascal.org/pub/fpc/snapshot/fixes/source/fpc.zip
The creation of the zip files is an automated process, and so these files are created every day.