TFS2010 for SSMS 2012 SSMS 2012 does not work with VSS 6. We installed modern source control, TFS 2010 server.

Then I Installed Team Foundation Server MSSCCI Provider 2010.
However the only choice for Source control  plug-in in SSMS 2012 is still  VSS6.
My VS2010 works just fine, I could connect to TFS in a team explorer.

How to add TFS as a second source code control plugin in SSMS 2012?
To use SQL Server Management Studio 2012 with Team Foundation Server (TFS) source control, you need to first install the Team Foundation Server MSSCCI Provider 2010 32-bit or Team Foundation Server MSSCCI Provider 2012 32-bit.

Then you will be able to select TFS as one of the source control providers under: Tools > Options > Source Control > Plug-In Selection.

Note that one of the pre-requisites to using the MSSCCI Provider is that you also have Visual Studio 2010 Team Explorer (the TFS client) installed on your machine. This is because it installs the TFS Object Model assemblies that the MSSCCI Provider uses to talk to TFS.