I bought one for my dog, and they told me he was a mutt - LOL.They offered a re-test for free, when they added more breeds about a year later... still said he was nothing, so he's either too "watered-down" or a very uncommon breed. Fun idea though, if it works!
You can buy them in some pet shops, like Petco I believe, and vet offices usually have a few versions...
I got mine online at this site: http://www.canineheritage.com/