Lakeshore Learning Materials has a Butterfly Nursery which comes with a coupon for three-five caterpillars. You can also by extra coupons for caterpillars. 800-428-4414

Monarch Watch sells caterpillars (14-16 Monarchs), T-shirts, seeds, posters, videos, and much more. 888-TAGGING

The Monarch Magic Company sells kits with Monarch caterpillars and a milkweed plant, books, videos, and much more. Order the caterpillars between the last week of April and the second week of September.