You can use Mercurial as client to their subversion repository.
Have you checked out hgsubversion yet? This allows you to have complete history in Mercurial.
See the details at : https://www.mercurial-scm.org/wiki/WorkingWithSubversion
It provides three ways of working with Subversion. Make sure that you use one and do not mix them.
- With hgsubversion
- With MQ
- Convert extension
[Personal Experience]
I have found hgsubversion better how ever it may have issues while converting the suversion repo to a Mercurial repo.
# This usually fails for a svn repo with
# large history or large files in revchanges
hg clone svn+http://.../svn local-hg
# If the above has any issues and dies before converting the repo, use hg pull
hg pull
Issue: You have an existing repo already.
- I guess the best way would be to create another Mercurial repo from the subversion repo using one of the methods above.
- Pull your change sets into this new repo from the older one to get all the changes and history from the previous one
- Now you are ready to submit the changes to svn repository