Where to find the installer for SQL Server Native Client 11.0.5058?

I am trying to track down some behaviour issues in our software which seem to dependent on the version of SQL Server Native Client in use. I have version 2011.110.2100.60 (aka 11.00.2100) but our client has 2011.110.5058.00 (aka 11.00.5058). I've been around the house on Microsoft websites, including MSDN, but I can't find a version more recent than the one I have. Is there a reliable repository of the different versions of the installer (sqlncli.msi) for testing purposes, or a guide to which versions are bundled with other products?