O comando apt-get source pulseaudio baixará os arquivos do pacote fonte atual e os extrairá automaticamente para você. Você encontrará o arquivo de regras no diretório debian dentro do diretório de origem recém-criado com o nome do pacote, eis como isso fica na minha instalação:
livewire@za20:~/Downloads$ apt-get source pulseaudio
Reading package lists... Done
Building dependency tree
Reading state information... Done
NOTICE: 'pulseaudio' packaging is maintained in the 'Bzr' version control system at:
http://bazaar.launchpad.net/~ubuntu-audio-dev/pulseaudio/ubuntu
Please use:
bzr branch http://bazaar.launchpad.net/~ubuntu-audio-dev/pulseaudio/ubuntu
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 1.468 kB of source archives.
Get:1 http://archive.ubuntu.com/ubuntu/ trusty/main pulseaudio 1:4.0-0ubuntu11 (dsc) [4.246 B]
Get:2 http://archive.ubuntu.com/ubuntu/ trusty/main pulseaudio 1:4.0-0ubuntu11 (tar) [1.392 kB]
Get:3 http://archive.ubuntu.com/ubuntu/ trusty/main pulseaudio 1:4.0-0ubuntu11 (diff) [71,8 kB]
Fetched 1.468 kB in 3s (455 kB/s)
gpgv: Signature made Fr 04 Apr 2014 09:40:46 CEST using RSA key ID 9B1A3456
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./pulseaudio_4.0-0ubuntu11.dsc
dpkg-source: info: extracting pulseaudio in pulseaudio-4.0
dpkg-source: info: unpacking pulseaudio_4.0.orig.tar.xz
dpkg-source: info: unpacking pulseaudio_4.0-0ubuntu11.debian.tar.xz
dpkg-source: info: applying 0003-esd-honour-system-pulseaudio.patch
dpkg-source: info: applying 0005-dont-load-cork-music-on-phone.patch
dpkg-source: info: applying 0006-load-module-x11-bell.patch
dpkg-source: info: applying 0016-nodisplay-autostart.patch
dpkg-source: info: applying 0020-stream-Return-error-in-case-a-client-peeks-to-early.patch
dpkg-source: info: applying 0022-inotify-wrapper-Quit-daemon-if-pid-file-is-removed.patch
dpkg-source: info: applying 0023-fixing_snd_mixer_poll_descriptors_count_when_zero.patch
dpkg-source: info: applying 0101-alsa-ucm-Make-combination-ports-have-lower-priority.patch
dpkg-source: info: applying 0102-combine-Fix-crash-in-output-freeing.patch
dpkg-source: info: applying 0103-resampler-Fix-peaks-resampler-s-channel-handling.patch
dpkg-source: info: applying 0104-default-system.pa-Do-not-load-module-dbus-protocol.patch
dpkg-source: info: applying 0105-sink-source-Initialize-port-before-fixate-hook-fixes.patch
dpkg-source: info: applying 0106-module-switch-on-port-available-Don-t-switch-profile.patch
dpkg-source: info: applying 0201-ALSA-Add-extcon-Android-switch-jack-detection.patch
dpkg-source: info: applying 0202-dont-probe-ucm.patch
dpkg-source: info: applying 0203-card-Add-hook-before-profile-changes.patch
dpkg-source: info: applying 0204-Add-module-to-talk-to-the-Android-audio-hal-to-set-u.patch
dpkg-source: info: applying 0205-suspend-on-idle-ensure-we-still-time-out-if-a-stream-remains-corked.patch
livewire@za20:~/Downloads$ ll pulseaudio-4.0/debian/rules
-rwxrwxr-x 1 livewire livewire 3346 Apr 4 2014 pulseaudio-4.0/debian/rules*
Então você pode encontrar o arquivo em pulseaudio-4.0/debian/rules , o número da versão pode ser diferente dependendo da versão do Ubuntu que você está usando.