I'm not familiar with green giant, but black magic doesn't make much of abulb, and are thus usually sold as growing plants. If you're interested in getting these wholesale, check out the link below. Their site is a little disorganized, but if you call them they can arange things, even less than the normal flats, for a slight premium. The tissue cultured plants are very small and need to be grown out in a greenhouse. If you are just interested in green elephant ears, walmart has plenty in the spring. For any more info, check out the aroid forum here at gardenweb.

Here is a link that might be useful: winterberry farms