Horn's Canna Farm is the best place, the cheapest price, nice rhizomes, about 25 varieties.

Karchesky Cannas has a wider selection, rarer varieties.

If you're just starting out, you might want to start with Horns.

Cannas are often hardy to zone 7, and maybe in zone 6 if you have a mild winter. I would suggest you wait til spring to acquire some and then plant them. If they multiply well for you, you might try leaving a few in the ground and carrying some inside for the winter so you don't lose all of them.

Here in zone 7a, mine survive winter if planted in a sunny spot that drains well in the winter. Altho they love water, the rhizomes will freeze in the winter in a wet spot.

I plant most of mine on a hill or slight mound. Then I mulch well. Even in our worst winters, most of mine have survived. But it's been a trial and error to find just the right spots in my yard.

If you look around, you probably have microclimates in your yard. Some areas will be colder, due to no walls protecting the area from northerly winds, or a lack of sun in the winter. Some areas will be warmer, like maybe the south side of your house if it's not shaded. If you have buildings, they can shield some of the cold. Brick walls in the sun tend to absorb sun and radiate heat. So this might be a great area for planting cannas to help them survive winter.

Hope this helps.

NancyAnn

Here is a link that might be useful: Horn Canna Farm