In KCKS, try Frontier Justice
https://frontier-justice.com/ They have an indoor range where you can try out (rent) guns as well. A bit on the pricey side, and they tend to the tacticool, but nice folks. They are also just across the highway from Cabela's which generally has a decent assortment of overpriced new and used guns and accessories. I haven't visited there for several months now, but it's right there at your destination.
South of the city, look at Olathe Gun Shop
https://olathegunshop.com/ They have a very good selection of new and used, with less emphasis on the plastic-fantastics. I know you mentioned being good on shotguns, but a while back they purchased a rather large collection of shotguns (mostly SxS) running the gamut from Stevens to the real high-end stuff. Worth a visit.
Not a gun store, but remember that Midway USA is right next to the highway in Columbia MO. You can order for pickup at their shop.
Have a safe drive.
