According to the information found on the developers website, Lockdown Browser is available to institutions that use Blackboard Learn, Brightspace, Canvas, Moodle, Schoology, or Sakai. Therefore, if your university is among those, you will have access to the program. For any other issues, contact your system administrator as he has access to the downloads.
Otherwise, access the following page and contact the developers directly, but they will forward your inquiry back to the university.