gpkcs-11 is free software, but it is not now an official GNU package. However, the GNU web site has long had this page about it. For more information and to download the software, please see the gpkcs-11 project page.
The project is moribund now; if you are interested in working on it, please contact the original author (Lutz Behnke). If the project becomes active, GNU would be happy to again consider dubbing it GNU.