Nels and Gerty

I am inquiring about a passenger list for family members from Oystre Slidre, Valdres, Norway. I found them on the digitalarkivet of Norwegians living in Minnesota in 1880 but cannot find them on a passenger list previous to that. His name is Nels Finkelson(age 54), his wife Gerty (age 46) and 8 children- eldest Mary (24) and youngest Peter (2). I was wondering when they came to America and on what ship. Any help you could give me would be most appreciated!! Thanks....... Betty Jean Ellingson