VisualSVN doesn't support multiple working copies within a single solution by design. Otherwise some basic concepts of Subversion such as atomic commits will be violated. However, there is a workaround based on the svn:externals property. The svn:externals property is a kind of link to another Subversion repository. Using this property you can incorporate code from several repositories within single working copy. For further details please refer to the Subversion documentation.