I couldn't find a tarball export option at the launchpad interface,
but you can browse the source and get individual files there:
http://bazaar.launchpad.net/~alf-rodrigo/cairoplot/trunk/files/head%3A/trunk/
But the bzr version in hardy should work fine for checking out the
source. I know that because I'm using it.
With bzr you can create a tarball like this:
bzr export cairoplot.tar.gz lp:cairoplot
hth,
--
Paul Eipper