Nicolai/Nikolay Olsen marriage date/place

I'm trying to find marriage date and place of Nicolai Olsen, son of Ole Johanssen Skaarslien and Anne Olsdatter, born 26 July, 1851 at Skaarslien (Gausdal) Norway. He married Mathiea Larsdatter approx. 1878 or 1879 in Norway. I believe they had 5 children, the first of which I found record being born 5 Nov.1879 at Skaarslien, another born 1880, 1882 and a fourth child born 1883 in Polk Co. MN. I'm not sure if the 5th child was born prior to 1879 or not. Nicolai, his wife "Mathea" and two of his children, Anna and Marie, came to America, leaving April 19, 1883, traveling with other relations. Anyway, marriage date and place and possible the other child is what I am looking for. Thank you, Dusty