I have rarely found common milkweed, but tell them you are looking for asclepias.
They may carry swamp milkweed, asclepias incarnata (which comes in many colors now, caterpillars don't care what color the flowers are
) and butterfly weed, asclepias tuberosa. I've even noted lately that at native plant sales another good place to pick up plants, in my area we are having several this month, have several varieties. I love native plant sales, cheaper than nurseries.
Plus, the tropicals, which depending upon your frost date will hold up better and regrow faster. If you have a sunny window indoors you can take them in for the winter. And, then you don't have to buy them. They are also easy to start from seed in the spring or summer.