There is an Apache 2 licensed tool called Polarion SVN Importer. Has anybody the sources for this and would put them on Github? I guess Apache License gives the right to do this.
The tool can be downloaded at polarion.plm.automation.siemens.com but there are no sources available.
Looks like even if a software is open source, its sources can get lost.
See Recommendation on Tools to migrate from Clearcase to SVN?