Although the term “centrist” is somewhat vague, it appears there were eleven states in 2018 that had nominees of centrist parties on the ballot:
Colorado Unity; Florida Reform; Louisiana Independent Party; Minnesota Independence; Mississippi Reform; New York Independence and also Reform; Oregon Independent Party; Rhode Island Moderate; South Carolina Independence and also American; Utah United Utah; and Vermont Green Mountain.
The best showings for these parties, for either Governor or U.S. Senator (for candidates who were not also the nominees of a major party), were for the Oregon Independent Party and the Rhode Island Moderate Party. The Oregon Independent Party gubernatorial nominee, Patrick Starnes, got 2.86% of the vote even though he announced shortly before the election that voters should not vote for him, but for the Democratic nominee. The Moderate Party gubernatorial nominee, William H. Gilbert, received 2.71%.
For U.S. House, the best showing was United Utah Party’s nominee in the First District. Eric Eliason received 11.62% in a race with both a Democrat and a Republican.
For state legislature, the best showing was also a United Utah nominee. Michelle Weeks, nominee for State Representative, 51st district, received 39.05% of the vote in a two-person race.