Celtis occidentalis and Celtis Laevigata (sugarberry) are both excellent as bonsai. Celtis O can be found if you look at some area nurseries. Laevigata can also be found, but it's a more Southerly species. Celtis Occidentalis can be found in the woods around here. It interbreeds with Sugarberry, but I've found that sugarberry isn't quite as winter hardy as the main species. It gets twig die back in more severe winters.
Celtis occidentalis won't require extensive winter protection. Both species grow like weeds and are capable of pushing extra fine twigging.
Ive thought about western hackberry,i did not think they grew in these parts,do they look similiar to sinesis??I also believe Brett has some if i cant find some in the woods.Thanks Rockm