On April 3, the Idaho Secretary of State posted a list of candidates for federal and state office in Idaho this year, including independent candidates. See this link.
The only candidates that could possibly be added would be the nominees of a new party, if a new party happens to qualify in Idaho this year. The petition for that is due in late August. Parties already qualified in Idaho are Republican, Democratic, Libertarian, and Constitution.
The 3rd parties in Idaho seem to be lacking candidates. Is this a down year?
The Constitution Party had 4 candidates in Idaho in 2012, and has 7 this year. The Libertarian Party had 5 in 2012 and has 4 this year. Those parties may or may not have candidates for partisan county office, as well. County candidates aren’t on the state web page.