Your regular MLS would make them available to individuals who want them as investments. Your realtor will have to ask more questions about what the rent & expenses are and how that works out to a captalization rate. That’s what the investors are going to want to know. Look for an agent who regularly lists multi-family.
There are several things you can do to get your available properties in front of investors. As someone else suggested, have a Realtor list them on your local MLS.
You can also contact local real estate investment groups to list your properties on their website and/or publish in their monthly newsletter to members/investors (try in KCMO). Another one to try would be (Point 2 National Listing Service) which caters mostly to Realtors, but I believe now they also accept FSBO (for sale by owner) properties as well.
Craig’s list is always good, especially for the lower-priced investment properties.
Good luck, I hope this was helpful.