Check out:

Song Sparrow Nursery and
Silver Star Vinery

I've ordered from Silver Star Vinery and the root system is huge. My sister ordered from Song Sparrow and raved about them as well. The only thing is that their shipping is expensive.

I just received seven clematis vines from Silver Star today and the root systems are really big! They all look incredibly healthy, though Debbie prunes them back for shipping so you basically receive a big healthy root system and a few sprigs of clematis. I'm sure they're all going to take off like gangbusters based on the roots. Debbie is VERY helpful if you need any suggestions or information on clematis. Just can't say enough good things about Silver Star. Worth every penny, IMO.

Good luck!
Denise

Pruning back the vines for shipping actually helps them establish and put out even more vines in the garden so it is a very good thing although some people are bummed when they open the box.

Clems are not an instant gratification plant for sure.

I'd add Chalk Hill, Brushwood and Joy Creek to that list. I've ordered from all of the above and been pleased each time. Keep in mind that you pay for 2 year plants and their shipping. Maintaining a plant 2+ years in a greenhouse, then shipping that mass of roots costs money, but it's worth it for a stable plant that gives at least some gratification the first year!

From what I have seen of pictures from people in MI, you are in Clematis Heaven there, so look/ask around for a local source for a 5 gallon. The bigger the plant, the higher the shipping...