This is a crazy, but very cool, idea: Buy earthworm eggs and plant them in the ground like seeds. Let the little critters hatch and make magic in your soil.
I believe the species is Lumbricus rubellus. This is a little red worm that will thrive in fertile soil and compost piles, but it is not a deep burrower like a nightcrawler. It's also not necessarily the best worm for a worm bin; for that I'd recommend Eisenia fetida, the red wiggler, which is the kind most commonly sold by worm farmer to use in worm bins.
Available from Gardener's Supply Company