I haven't grown any from seed as yet. They do self-seed readily though... despite the tendency of ants to run off with the seeds (due to a nutrient-rich portion of the seed that they collect to feed on). The more commonly grown species (e.g. H. nobilis, H. transylvanica) are often available from plant nurseries in spring - of course, they are snapped up when in bloom. (When potted, as for sale at nurseries, they go dormant after flowering - odd as they don't do this in the garden.) You'll be glad to know that they are very undemanding in our climate - they flourish in shade to part shade, and are not at all fussy about soil conditions, nor about moisture. (I've never seen mine show any signs of water stress, even when other, more sensitive, species around them clearly were.) I grow the species mentioned above, a couple of doubles, and some fancy-leaved hybrids. I should mention too that my mother grows H. nobilis in rural zone 2, which is a good indication of their hardiness. Gardens North is currently selling seeds of H. nobilis v. obtusa (formerly H. americana) - acckk, more renaming! Plants are easier to come by than seeds, e.g. Fraser's Thimble Farms - Japanese fancy-flowered types. Be aware that if you end up getting seeds through trades, that dry storage is thought to be fatal, so seeding results may not be completely successful (i.e. seeds should be picked as soon as ripe and stored moist).
Aside from Garden's North and Thimble Farms, Rundle Wood Gardens here in Calgary (http://www.rundlewoodgardens.ab.ca/) usually also has a couple of cultivars for sale.
Thanks I have checked these out. I am not in the Thimble Farms price league so will rely on seeds I think. It is the season for the "seed itch"! Clayton