The Mardens stores in Lewiston and also Waterville also carry wonderful fabrics. Another great shop in Madison is The Fabric Garden, think that's the name. It is right on the main road from Skowhegan, ME to Madison and has a wonderful assortment and wonderful staff.
There are several other shops right on the coast and you get to explore the coast of Maine as an added bargain. Bar Harbor, which is home to Acadia National Park, also has a lovely quilt shop as well as tons of other shops to explore.