In Springfield, MO I've seen a total of 6...ever.
There was a local guy that has owned 2 of them, one of which (Berlina) got passed around to a couple of other locals, and the other (Silverstone) got totaled, unfortunately. (CTSC model...and in the rain at 30 mph, no less)
There was a Dodge Viper meet that I attended where there were about 5, but they weren't from our area, so I guess those don't count.
There was a guy in Aurora that had one(New Formula), but recently sold it to a buyer in PA.
There used to be a Rio in town, but I've not seen it in 5 years or so.
There was a Kieser that was passing through and needed a tire, and I pulled up to work just as he was leaving. That was a couple of years ago, so I'd say it's been that long since I've seen another one.
Mine...GPW.
I've heard of a couple of other New Formula cars in town, but I've not ever seen them in person.
It would be nice to find a couple of other owners close by, but I'm thinking that if they are in fact around somewhere that they aren't on here and never bring their cars out.