From cooking.com:

Scallions are also known as green onions and refer to a distinct variety of immature onions. The vegetable has a white base that has not fully developed into a bulb and green leaves that are long and straight. Both parts are edible. Store in the refrigerator, wrapped for up to five days. They can be eaten raw or cooked in numerous dishes from soups to salads.

You should be able to find these in the produce section.

Shallots look like yellowish garlic, and their flavor is a cross between onions and garlic.