Arsenal Factory (subway Arsenalna) has a shop with new Kiev cameras (when I was there, though, only medium format and the nikon-mount slr). Worth a visit though, because of the history of the factory.
There is a photo store on krasnoarmeislaya (subway Palats Ukraina) too, whith quite a good selection of used equipment (as well as new)...other than that, it's markets and tourist streets (such as andriyskiy), but i'd stay away from buying those...they are often in terrible shape.
Regular camera/electronic stores with decent selection of new stuff are everywhere, especially around the Petrovka shopping area (subway Petrivka).