The Pgpool-II 4.2.0 sources can be obtained from the download section of our website: http://www.pgpool.net. You should get a file named pgpool-II-4.2.0.tar.gz. After you have obtained the file, unpack it:
tar xf pgpool-II-4.2.0.tar.gz
This will create a directory pgpool-II-4.2.0 under the current directory with the Pgpool-II sources. Change into that directory for the rest of the installation procedure.