There's a store on the NE side of Columbus that infrequently gets Neo stuff in. Video Games Express. It's off of st. rt. 3 off of I-270. Also, there's a shop on the east side on US-40 a few miles west of I-270 that tends to have some oddities every once in a while. No Neo stuff the last time I was there, but lots of odd TG-16 stuff, and he said that he tries to get Neo stuff. I know that Neo stuff floats around in Columbus b/c there were a few stores that used to rent Neo cart systems out, the store on st. rt. 3 being one of them.
I don't know of any good stores in Dayton or Springfield. The store in the plaza across from the Springfield Mall has next to nothing good, though I guess they're buying older stuff now.
There's a guy at the Caesar's Creek flea market that can maybe get some stuff for you. His 8 and 16 bit selections are pretty good and usually fairly priced as well. He's usually outside but may be in the newest area of the indoors section.
On the arcade stuff, I'm not sure anymore. There used to be a great arcade on High street in Columbus on the OSU campus that had an MVS with Bomberman, SS4, and something else that I don't recall. Unfortunately, it's closed now. They had a SSF2T machine until the day they closed IIRC, and the competition was pretty good.
I was distraught when I went into the Springfield mall a few weeks ago and the 2-slot MVS with Strikers Plus was gone...and Zero Gunner disappeared a few months ago.