The arguably healthiest discipline of bicycle racing/sportif in the United States offers a full calendar of events in the Kansas City region.
The information about events is a little diffused, but here are some links that we find helpful.
KC Gravel Grinders Facebook page. Frequent postings for events and local group rides.
GravelCalendar.com Lots more than just our region, but easy to find by pinpoints on the map.
BikeReg This registration service is used by a fair amount of organizations. Searchable by region and state.
MWGCA Another Facebook page focusing on Midwest Gravel cycling
Your local bicycle shop is often tuned in to group rides and upcoming events as well.