I have grown out gingers from grocery store tubers before. Make sure they look firm and nor shriveled. It's worth a shot. As for growing a cultivar where you know the name . . . Ebay, online garden company websites are all I can think of.

As mentioned, ginger rhizomes(?) from the grocery store will grow fine. I have done the same with tumeric from a health food store. I soak each in warm water for an hour or so to try to wash off any sprouting inhibiters. I'm going to ask a friend in Los Angeles to look out for galangal in Asian markets, as I can't find it fresh in stores or mail-order nurseries (one may be able to find it seasonally fresh for consumption by mail order; I haven't looked recently). I'd like to find grains of paradise and the real cardamom as well.

I've had luck at the Asian markets myself. I have also grown ginger. I had a ginger plant for many years. Here is a picture of my home in westerville. If you click on the link you can see my garden. Its the featured one on the page.