The deadline to file for the Alaska primary is June 1. Here is the list of candidates so far. Two Libertarians are opposing each other in the Libertarian primary for U.S. House. It is somewhat unusual for minor parties to have contested primaries for Congress. The two are Jim McDermott and Jon Briggs Watts.
Nominees of unqualified parties, and independent candidates, have until mid-August to submit petitions to be on the November ballot. Thanks to Michael for the link.