I am in West Tennessee...... I have noticed that I have no Honey Bees, haven't seen one in a couple of years, since I am in the middle of a large agriculture area I suspect that is the reason for no bees, but the vegetable garden and the rest of the annuals are doing greathttp://www.hardytropicals.org/blog/entry/harvesting_seeds_from_colocasia_gigantea
Also Cannas do produce seeds. They are available on-line.
Of you are not getting seeds from your plants then the pollinator is absent. Some plants require only certain species of insects for pollination. If the plant is too far North of its natural range these pollinators may not be around.