A couple of options. Call the Bozeman Police Department and ask them if you are allowed to legally purchase a firearm as a citizen of Norway on a student visa. If they don't know they should be able to give you some contacts for who can. You can also try the Gallatin County Sheriff's office. Another possibility is calling a sporting goods store in Bozeman like Powderhorn Outfitters or Bob Wards. They sell firearms all the time so they're familiar with the paperwork requirements. If you're allowed to buy one just pick one up when you get there and then just sell it before you leave if you don't want to take it back.

The other option I can think of is to go through the hunter safety course, get your hunting license and have somebody in Norway ship your rifle to you (presuming Norway allows that). It would have to be shipped to an FFL (Federal Firearms License) holder (usually a sporting goods store or gunsmith) and they charge a minimal fee to process the paperwork and give you your rifle.

The thing is just call around and ask questions.