1. download the two source tarballs from the auto-build site (pick a date): http://autobuild.puredata.info/auto-build/

2. run these commands in your Terminal:

sudo apt-get install dpkg-dev devscripts debhelper
tar xjf Pd-extended_0.43.1~20120928-source.tar.bz2
mv Pd-extended_0.43.1~20120928-source.tar.bz2  pd-extended_0.43.1~20120928.orig.tar.bz2
cd pd-extended
tar xjf ../Pd-extended_0.43.1~20120928-source.debian.tar.bz2
debuild -uc -us

If you want to generate a source package for uploading to a build service like Launchpad or OpenSUSE Build Service, run debuild -S -uc -us. Then you'll have a complete source package with all the files needed in the folder below where you run the commands, were the tarballs and the pd-extended/ folder are.