Hi Benny,

You shouldn’t have too many problems finding a cardboard bike box in Bergen.

Try the sports shops in the center and if they can’t help the large XXL stores usually have plenty: http://www.xxl.no/store-finder/sportsbutikk-bergen/lagunen
You also have Trek Bergen, who should be helpful: http://www.trekbikes.com/za/en_ZA/store/405995/

Full information about obtaining a bike box can be found here: http://www.cyclenorway.com/bike-box-travel/