fwiw:
# ls -d1 /usr/ports/*/*zlib*
/usr/ports/archivers/fpc-paszlib
/usr/ports/archivers/hs-zlib
/usr/ports/archivers/hs-zlib-bindings
/usr/ports/archivers/hs-zlib-conduit
/usr/ports/archivers/hs-zlib-enum
/usr/ports/archivers/jzlib
/usr/ports/archivers/lzlib
/usr/ports/archivers/php5-zlib
/usr/ports/archivers/php53-zlib
/usr/ports/archivers/php55-zlib
/usr/ports/devel/fpc-zlib
/usr/ports/devel/mingw32-zlib
/usr/ports/security/find-zlib