I have big plans to document all of the good places in New England that I have found to contain great old tools for sale. Check back often, and hopefully I haven't procrastinated too much and actually have something to read.
Hollis Flea Market This is the best flea market I have been to, and it usually has at least a couple really great tool dealers. Make sure to get there early, because I may just beat you to all the user tools!
Jonesport Wood Co. I have not actually been to any of their locations (there are three in all), but from what I have heard from friends and seen online this is by far the best place to go see an enormous selection of user hand tools in person. They also happen to be close to Lie-Nielsen Tool Works.