September 8 was the deadline for independent candidates to file for the North Dakota ballot. Two candidates submitted signatures for US Senate. One is the Libertarian nominee, Roland Riemers. The other is a true independent, James Germalic, who was also an independent candidate for U.S. Senate in Oklahoma in 2002.
The nonpartisan politics1.com does not list these two independent candidates on their ND website and the ND Sec of State does not seem to have them listed as being on the ballot.