have you considered planting one from the grocery? (organic)? In the past, I've ordered from Steele and (I think) Southern Exposure Seed may have a few left.

Isn't it too late to plant Sweet Potatoes? I grew mine by putting a potato into a glass, held up by toothpicks, and letting the slips grow from there. I cut the long vines into sections with at least three nodes, plus a long tip shoot. I put those into water to get some roots (they root in just a few days), and then planted them out. My purples are going mad, but my reds aren't growing much at all.

A little late, but maybe some small tubers. I think they need about 100 growing days. I plant in June/ early July. This year I must have had roots unpulled from last season - surprise crop! but they aren't nearly as lush and full this year.