Sunchokes are a species of perennial "sunflower," which are members of the aster/daisy family (Asteraceae). It is a very large plant family, and Black-eyed Susan also belongs to that family, though the two plants are not in the same genus and are not closely related. Extension doesn't keep track of plant supplier offerings, so we don't know which nurseries (local or mail-order) offer sunchokes in their inventory. A more niche vegetable like this might need to be sourced at a mail-order nursery since they often specialize in particular plants (like edible plants in this case), but you might have luck asking vendors at a farmer's market if they grow the plant and if they sell tubers. (The plant can be somewhat weedy in its vigor, so they might even give a few tubers away.)

Some grocery stores do periodically stock the tubers in the produce section (for cooking/eating, not for planting), but we don't know if any treatment or chilling they might have received post-harvest would interfere with growth if they were to be planted. (Plus, just in case they carry asymptomatic diseases, it's best to grow new plants from seed or nursery-grown transplants of young sunchoke plants, to avoid the risk of growing a contaminated plant that can't be treated. Reducing the risk of disease is why, as an example, garlic should be grown from cloves sold for planting and not cloves from a grocery store-purchased head. The same might apply to sunchokes.)

Miri