Here's a list of sources if you're looking to get some kefir grains to make your own at home. (Thanks Panmeli!)
Scroll to the bottom for the United States. (This list is based in Canada so we're in alphabetical order instead of getting our country automatically at the top. Humbling, no?) Then, look for sites close to you at a price you like.
I haven't ordered anything from these people, but at least one of the Chicago sources offers to let you pick them up instead of paying shipping. And seriously, if you're looking to run a scam, I'm going to guess kefir grains aren't a big money-maker.
Lately, I've been buying smaller sizes of fat-free kefir to make creamy dressings out of. We use the peppercorn salad dressing mix from The Spice House in Geneva, mixing it with kefir and a bit of rice wine vinegar. It's a bit runnier than the mix The Spice House suggests (half sour cream, half mayo), but a bit more natural and with much less fat.
And unlike the kefir sources, I can vouch for Spice House. In person or online, I've always had good experiences. If you try their spices, you'll wonder how you ever settled for the blah alleged spices you get at the supermarket.
Don't remember what Kefir is. Read this (especially the reader comments as they school me).