Just got back from a Scandinavian trip, and Garmin found me some great campsites. However, sometimes helps to do as above,(ie "POI's/Lodgings" and when you open the "Lodgings" window, type "Camping" into the search box. You can also chose from options of "close to present location, or "On present route", or "close to destination" etc.
Archie's Campsites is also useful, but always doubtful as to how current that list is.