Using git-svn for clone, fetch ect. does not work. I never tried this before, but according to Blogposts for Version 1.4 a while ago git-svn at least was supported.

When I enter the URL, I'm asked for credentials and authentication works. After that Sourcetree tells me that it is no valid URL. Details show these error:

Command: git -c diff.mnemonicprefix=false -c core.quotepath=false --no-optional-locks ls-remote <myrepo>
Output:
Error: fatal: repository '<myrepo>' not found
Command: perl.exe <SourceTree-InstallPath>\tools\svn.pl info <myrepo>
Output:
Error: System.ComponentModel.Win32Exception: The system cannot find the specified file

Trying to install perl did not help and had no effect on these errors.

I performed the clone command on git bash and it worked. I could add the cloned repository to Sourcetree, performing a pull or fetch does not work. Sourcetree seems to hang on the authentication:

git -c diff.mnemonicprefix=false -c core.quotepath=false --no-optional-locks svn fetch
Authentication realm: <myrepo> VisualSVN Server