To answer the question, yes, there are two second-hand stores in Newcastle of which I am aware. I don't know the names, but one is by Pizza Hut; the other is on the Main drag near the Smoke Shop.
The store by the Pizza Hut is a good little store, and the prices are great. She takes consignments too. A car drove through the side of the store last winter and it has not been repaired yet because the building owners are waiting for the insurance co. Therefore, her stock is really low now.
The 7th St. shop on Main street has lots of stuff, but much is sold as "antiques" and is higher priced than I'm willing to pay. The owner is a really nice guy and loves to visit. He's got a beautiful Black Labrador too.

Don't go in wearing anything that won't survive dog drool.
Newcastle used to have a monthly "farmer's market" in the summer, but I've heard nothing about it this year. Little or none of the things offered for sale there actually came from locals, and the prices tended to be higher than the grocery store. This town could certainly use a true farmer's market. Don't know where we'd get the farmers...
We do have a produce co-op deal here, though the fruits and vegetables are from standard commercial growers all over. Organic baskets are also available at considerably higher cost. Delivery is every two weeks, and you must go pick it up within the given time frame. http://bountifulbaskets.org/ Look here for more information.