You can install gzip on your AIX system by copying gzip from another AIX system via FTP.

cd /tmp
mkdir gnu
cd gnu
 ftp ftp2.netscape.com
 cd /pub/unsupported/gn
 bin
get gzip-1.2.4.rs6000-ibm-aix3.2.tar.Z
 quit
 uncompress gzip-1.2.4.*.Z
 mv gzip-1.2.4.* gzip