During the summer, you can get them in the Farmer's market on Edgell Road. They're super cheap, too - $3.00 a bag! I was excited when I discovered them last summer because they can be quite expensive at the markets.
also at union sq and harvard sq farmer's markets during growing season. for now though, and for proximity to framingham, i'd second cheryl h's russo's tip. plenty of other great stuff to buy while you're there as well.