There are a few places you can order on-line. I like going bananas (http://www.going-bananas.com/) or eBay. If you are not trying to get fruits, basjoo could probably survive outside in your zone (may die down during winter and come back when the weather is warm). A few other dwarf bananas for potting are dwarf cavendish, dwarf orinocho, and dwarf Brazillian...

You might consider going with a Superdwarf-type Cavendish. They would stay the smallest. You needn't worry about pollination at all. Most edible bananas are seedless anyway.

You'll have to consider where you're going to keep your banana for the winter. Keep in mind a greenhouse with warm, humid air and high levels of light is optimum for growth over winter. If you have a heated garage with just a bit of light that stays cool, but above 45 degrees, you might try to keep it alive in there -- in nearly a dormant state with little water. The cooler temps will limit spider mite proliferation.

In a heated, sunny room in the house it's likely going to be plagued by spider mites which you'll be battling most of the winter.

If you want one for fruit the ones that Dave, and Winsorw would work for you, but you'll need at least a 15 gallon pot for most of them(minus the super dwarf cavendish).
Personally I like the small ornamental flowering types that are grow for their flowers, like Musa manii, Musa veluntia, Musa ornata(many different colors), Musa laterita. Ensete superbum is also good in a pot and easy to sprout from seed.

I've got my raja puri in a 20gal bucket I got for about $6. I pulled it inside the other day because for the storm since we were supposed to get 40-50mph winds most of the day and oddly it was easy to pickup and move inside but I had to slide it back out ;) My self watering containers wouldn't budge for me and they just got put up against the house and covered.