score:5
You can get it in Keflavik airside. There are service desks in Terminal C (near gate C22, arrival from EU) and Terminal D (near gate D15, departure to US)
https://www.icelandair.com/support/pre-flight/connecting-at-keflavik/
You will ordinarily receive a boarding card for each flight. If you do not have a boarding card for your second flight, please contact the Icelandair service desk representative at KeflavΓk airport.