Aside from finding a guy who has a band mill and works out of his garage, there's really nothing particularly close by. Rugby/Downes & Reader in Stoughton, Highland in Brentwood NH, Forest Products in Greenfield, Rex or McIlvain in CT if youre buying quantity. For smaller quantity and really good (and pricey) quality I'd go to Forest.

edit: all these places sell in the rough - your options for dimensioned might be somewhat limited (I always bought rough, so not entirely sure).