Devils Due Publishing (DDP) is no longer selling issue one.
You can still order a five issue subscription (2-6) to the Jericho comic via DDP: Link
If you missed issue #1 you will be able to find resellers of new and used copies via Amazon or EBay: Link, Link
The paperback version of the 6 comics will be available AFTER the 6th issue is released. Amazon has it listed and you can sign up to be alerted when it is available: Link