Birth and Marriage Records

I would like to find the birth records for Kristiansund, Norway for 1867 and 1870. I would also like to find the marriage records for Kristiansun in 1888. These were the birth years and marriage years of my grandparents. I'm hoping that finding this information would give me information about my great grandparents. My grandfather Albert Olsen was born Dec 18 1867 and my grandmother Bertina Larsen was born Feb 18 1870. Any help on finding information about earlier generations would be appreciated. Mary McWilliams