They're actually perennials, so as long as it's not frosted over, they're always in season. (Even if it is frosted over, they can flower in a pot on a sunny window sill indoors.)

I live in Australia, so I don't know where you can buy them, but if you know anybody who's growing them, perhaps they'll share some cuttings with you.
They grow well from cuttings; I put mine in water to grow roots before planting.
Over the first couple of days, they will wilt badly, but don't worry because they perk up again after about three days.