Missouri has 9 U.S. House districts. Filing closed recently for Missouri primaries. The state has 3 ballot-qualified parties, each of which nominates by primary. This year Democrats will have a nominee in all 9 districts, Republicans will have a nominee in 8 districts, and Libertarians will have a nominee in 7 districts.
In 2006, all three of those parties had nominees in all districts.
New parties in Missouri still have plenty of time to petition their way onto the ballot. The Constitution Party has already finished its petition, but hasn’t handed it in yet, until it finishes recruiting candidates. Independents are also free to file in late July.