I had no success googling this and thought it would be better to try here before contacting embassies.
Although an extradition treaty is required between the US and some other requesting nation, that may not be the case with Norway. There is a law pertaining to extradition, the current version being here; an English translation of an earlier version (not significantly changed) is here. That law spells out the general conditions for any extradition, so a specific treaty is not required by Norway. I don't know of a place that lists all of the treaties of Norway.