You can often buy little packets of Triops eggs at hobby stores. There are a few places around town that sell them.
Back when I was teaching middle school science I had a bowl of the things. They were really neat to watch once they grew to size. Very aggressive little things, too. They would really attack the little slivers of carrot I threw in there and would cannibalize each other whenever one died.
One of the really cool things about Triops is that they almost always lay eggs into the sand of their container before they die, so you just drain the water, let the sand dry out for a week or two, then add more water and hatch a new batch of shrimp.
This went on for 3 cycles until a girl spilled a box of salt into the sand, ruining the culture.