So this weekend I discovered that SVNBridge is working fine now.
I haven’t tried it against our production TFS server but against codeplex it works great.
SvnBridge - Use TortoiseSVN with Team Foundation Server
SvnBridge allows you to use TortoiseSVN and other Subversion clients with Team Foundation Server. It converts the calls made by your Subversion client to the API supported by TFS.
SvnBridge works by running an executable on your local machine that acts as the bridge to TFS. You point SvnBridge at the TFS server, and point TortoiseSVN at the bridge running on your local machine. This allows you to use TortoiseSVN with any TFS server without needing to change the TFS server in any way (no need to convince your system administrator of anything!).
If you haven’t checked it out already, it’s definitely worth a look.