To harvest the scape, break it off close to the heart.
Most people that grow garlic will have scapes, but taking them to the market to sell is another thing. They don't make a lot of $, so I think a lot of people don't bother. They are great as fresh garlic, in salad dressing, soup, garlic pesto...etc. You can treat them like any other garlic. Ask at your market if the vendors have any. I've not ever seen them in a grocery store.
My day off yesterday was great. Some random food shots: