Easy to grow from seed especially if you want a specific colour/variety. They are slug food IME so do protect. It is probably too late to get a reliable germination this late in the season, but you could try sowing some now, under cover/in a coldframe.
I'd also buy some plants as well, as the seeds, if they do germinate they wont flower well until quite a lot bigger & the colder weather/less light will prevent that happening. J.