Last Updated: Dec 20, 2017
National strategy documents are available in the Homeland Security Digital Library (linked below). You can access them without an account but you will find the site more useful if you request an account so you can specifically review the National Strategy Document section and be able to search the full site. Account registration criteria and other information is available at the link below.
You can also look at the NDU MERLN [Military Education Research Library Network] site where they maintain copies of all the national strategy documents (linked below)