Resources for 6th grade common core social studies

I am the mentor for a new 6th grade social studies teacher and she is having trouble finding text resources for the early civilization curriculum under the new common core standards.  Due to funding our sixth and seventh grade teachers are working without textbooks and have expressed difficulty in finding age and reading level appropriate sources, especially primary sources.  I teach 8th grade US history and this is never a problem for me and I can help her with projects once we come up with the materials.  Has anyone else run into this problem and are what solutions have you come up with?