See the main site http://www.gzip.org/zlib/ for places to download the 
complete sources.  Currently based on zlib-1.2.1

Note that these are not the complete zlib sources - the following
directories have been deleted since they are irrelevant for the
eCos support:

amiga/
as400/
contrib/
msdos/
old/ 
qnx/ 
win32/

Additionally, local changes has been made to the remaining files. Code
changes are marked by __ECOS__ (comments or definitions). Finally, the
headers zlib.h and zconf.h have been moved out of the directory into
../include.