There are two I go to on occasion, though neither would I really recommend. I buy 99% online now.
The place in Woburn is staffed by people apparently far too busy/important to help a customer looking to spend money. I won't go back there again.
Cambridge is OK, and the better of the two, though the staff can be a bit sketchy. It is Cambridge, so I guess that comes with the territory.
They do have a decent selection and all grains can be bought in the exact quantities needed. I've called to ask about specific items and been told "Yep we have it." Upon arrival it is a different story.