I actually found a box of 24 ga shotgun shells recently. Twenty-four gauge shotguns? No.
As others have said, get a light load for a 20 gauge. The men in my family preferred the 16 gauge -- in their era, the 16 was very popular. Me, I've never owned one due to 3" mag 20 ga ammo.
Don't get me started on the proliferation of all manner of new rifle chamberings. Totally bizarre. Precious few have anything new to offer over cartridges that came out 70+ years ago. We certainly need not develop new shotgun gauges nor resurrect chamberings made obsolete. Too, those who reload can come up with all manner of diversity with already available rifle and shotgun casings.
No offense intended, but many hunters simply need to hone their hunting skills. For OCD target shooters, I actually CAN see wildcat cartridges -- but that's on them, they're not asking the world to revolve around them. They are do-it-yourselfers; certainly nothing wrong with that.