My research indicates, these symbols comply with "ISO 1219 - BS 2917" standards.
However, please note that these drawings are provided as sample files only and may not be appropriate for commercial pourposes.
If you are looking for alternatives libraries you may ask your local reseller, if they have some on offer. I also included the following sample link that seems to offer a full library that can be used with AutoCAD. - http://www.simplecad.com/iso-1219-symbols-bs-2917.htm