If you follow upstream Git development closely, you may have noticed that the Mercurial and Bazaar remote helpers (use git to interact with hg and bzr repos) no longer live in the main Git tree. They have been split out into their own repositories, here and here.
git-remote-bzr had been packaged (as
git-bzr) for Debian since March 2013, but was removed in May 2014 when the remote helpers were removed upstream. There had been a wishlist bug report open since Mar 2013 to get
git-remote-hg packaged, and I had submitted a patch, but it was never applied.
Splitting out of these remote helpers upstream has allowed Vagrant Cascadian and myself to pick up these packages and both are now available in Debian.
apt-get install git-remote-hg git-remote-bzr