2nd great grandfather not showing up on immigration records or passenger lists

I am searching for the immigration records for my 2nd great grandfather, Leger Alfonse Vogel, and his family. They came to the United States from Alsace-Loraine in the early 1870s. The 1880 census in Iowa says that Leger Vogel and his wife, Frances Hartmann Vogel, arrived in 1870, but it says that three of their five children arrived between 1872 and 1875. So I am not definite on the exact years; but somewhere between 1870 and 1875, when their 4th child was born in Missouri. Their fifth child was born in Iowa, and then the whole family is on the 1885 Kansas state census. The three children that came over from France were Julia Theresa Vogel, James Alfonse Vogel, and Marie Eugenia Vogel. The two children born in America were Melanie Vogel and Frank Jospeh Vogel. I have copies of the naturalization records for Leger Vogel, which are located in Iowa, but can't find naturalization papers for any of the other family members. Leger's papers give no indication of arrival date or port, or of ship name or departure port. I have looked at all the passenger lists that I can find online and have come up with nothing. Can someone with more experience with immigration records steer me in the right direction? I can't believe that I can't find a trace of any members of my Vogel family who came over to the states from France. Any guidance would be very appreciated. Thank you!