You can buy the Nortrip Guide in two places in Norway:
In Nortrip's webshop you can pay both with bank card and with Vipps (Norwegian mobile payment option). You will automatically receive an e-mail with your membership number, so that you can start using the app right away. The app includes a membership card, and you can immediately start visiting Nortrip hosts. The Nortrip Guide is normally shipped within one working day. The Norwegian Postal service estimates a delivery time of 4-9 days within Europe.
If you are already in (or on your way to) Norway and would like to have the Nortrip Guide in book form right now, you can buy it at most of Ferda's departments (with the exception of Trondheim, Nordkjosbotn and Vinterbro).
For an overview of all Ferda's departments, see Ferda's web page.