I got'em from Petco. They are wingless fruit flies (Drosophila Melanogaster) - but it's quite funny - the species IN the jar is wingless... and the species pictured ON the jar has wings!
They come in a jar with a special fine mesh screened top, some 'starter' culture on the bottom and what looks like with paper-ish Easter basket 'hay' inside.
Who makes up these jars? The Fruit Fly Company, of course. No, I'm not kidding. That's the company's name and they're in Washington state. Hooray! American Fruit Flies!!!
All you do is buy the jar, and the flies do their thing. The culture lasts for 3-5 weeks, according to the manufactuer.
I suppose one could look up how to make the culture, and transfer flies to a fresh culture jar to keep the little buggers going... or you can buy a fresh jar at the store after the first jar 'peters out'.
I'd personally buy two jars (the second one about three weeks after the first), so when the first colony dies you can prepare a new culture in the first jar. When the second colony is dying, they can be moved to a fresh culture.... and so on, and so on.
The above link is to a page on the starter culture recipes... I'm sure there are others out on the web.