They have taken it out of the ribbon in 2013's 2D Drafing and Annotation workspace. You can type GROUP in the command line or customize your CUI.
If you open AutoCAD Civil 3D as AutoCAD from the Start menu, you will have Groups in the ribbon.
I have not been able to do it successfully. It's not going to be easy because the 2D Drafting and Annotation workspace actually uses the Map.cuix file.