Bluestone perennials lists blue-flowered plants for sale (see link). I've grown them in the ground, where they seem to act like biennials. One did come back after the winter, but I stepped on the exposed part of the root system accidentally, and that was that. Not a tough cookie :-( They did send up many 4-foot flowering stems that all needed staking. The seeds only sprout when ripe, which of course is when campanula immediately drops its seed.

My understanding of the colonial potted tradition is that the pots were left out of doors until the plants set buds, then carried inside and placed in the fireplace while blooming. They need full sun to set buds.

Here is a link that might be useful: Campanula pyramidalis plants

Thanks so much for the information! I ordered my Chimney Bellflowers as well as some other blue flowers (my favorite)!
Shelley