You might think that it would be hard to build a Debian package maintained in Subversion that you've checked out using bzr-svn; I certainly couldn't find anything actually about it when I searched for
bzr-svn svn-buildpackage, whereas for
git-svn svn-buildpackage I found some stuff obviously about that (but which didn't turn out to actually work).
However, it looks like the real reason nobody seems to say much about this is that it's actually drop-dead easy: just use bzr-builddeb as if it were really just a bzr branch! (It certainly seems to work with
Hopefully, this blog post will aid future searchers, even if I don't have much google-juice…