I suppose "native to where?" is a good question. I love our natives (to North America) and try to use them as much as possible. The Native Americans took plants with them all over this continent and we have a few species of Yucca and Opuntia (prickly pear cactus) that occur in Tennessee. One good one is called Chickasaw Plum. It's Prunus angustifolia. I'd call it a good native substitute for Prunus mume as it has small white flowers and craggy bark. It too was likely moved around by the locals as it occurs from central Florida up into New England from what I've read.
Deciduous winter flowering species are my favorite and I'm on the hunt for more. Hamamalis vernalis, our native Witchhazel is a nice one. Amelanchair arborea, our native Service Berry is another as RockM said. As for others native to this side of the continent, there are a few that I haven't seen used for bonsai much. I'm looking into the matter now. I believe there are a few species of Hawthorne that flower in winter.
As for kusamono, this is another matter I've been looking into. Visit native plant nurseries throughout the year as I do and you can see some interesting stuff; the flowers on many are short-lived for sure. I've been looking into some native mustards and other cedar glade plants that grow on granite out-croppings.