G-Wrap can be obtained from the main GNU archive site http://download.savannah.gnu.org/releases/g-wrap/ or any of its mirrors. The file will be named g-wrap-version.tar.gz. The current version is 1.9.15, so the file you should grab is:
To unbundle G-Wrap use the instruction
zcat g-wrap-1.9.15.tar.gz | tar xvf -
which will create a directory called g-wrap-1.9.15 with all the sources. You can look at the file INSTALL for detailed instructions on how to build and install G-Wrap, but you should be able to just do
cd g-wrap-1.9.15 ./configure --prefix=... make make install
This will install the G-Wrap files in <prefix>/share/guile/site/g-wrap.