Thanks for writing. 'Niobe' clematis is a hardy variety that should thrive for you. I'm not sure why you're not seeing that variety very much in your area --- it could just be that suppliers around you prefer different colors or different varieties. But I have 'Niobe' thriving in my garden in Zone 5 and I grew it well in Minnesota (Zone 4), as well.
---Justin, Senior Garden Editor, BHG.com "