If you're still looking for AutoCAD Portable 2012 64-bit from third-party sources:
AutoCAD Portable 2012 64-bit offers many of the same features as the installed version of AutoCAD 2012. Some of its key features include: autocad portable 2012 64 link
Given these points, if you're looking for (not specifically the portable version) for legitimate use: If you're still looking for AutoCAD Portable 2012