Try Gurney's, Jungs or Richters catalogs.

You can grow sweet potatoes by letting the store variety develop eyes, then cut into generous portions including the eye, dry very briefly (a day), and plant with the eye just below surface level. If the eye has grown a few inches, bury the growth about half-way. This works with any tuber, including J.Artichokes. We did it with blue potatoes when the kids were small & what a kick they got out of digging them up! Harvest when tops die back.

Thanks for the suggestions! I know how easy it is to make a houseplant by suspending a sweet potato in a glass of water (and then standing out of the way while the vine shoots up!) but it didn't occur to me to try it in the garden. I'll give it a try! There's a variety of sweets in the grocery, some long and slim, some yellow, some orange, some fat and blunt; not sure which are best suited to this area a but I'll try several kinds. I assume they're not treated like potatoes are to prevent sprouting. I think I'm stuck with ordering the Jerusaken Artichokes by mail though. With the cold and snow today, it's hard to realize that it's now March and planting season will be here soon- but guess I should get that order in!