I think the Yankee Artifacts guy operates out of the location now-building with brick facade just before the intersection of Rte 9 & 20 westbound in Shrewsbury/Westborough line.
I don't think he does retail/walk-in business, he has a web site by the same name (Yankee Artifacts) which he sells used pistols and rifles and does the transfer through your FFL.-I have bought a rifle from him and had to go to my FFL to do the transfer. I work in that area and stopped by after hours one time and could see some stuff locked up inside but they had signs up indicating no retail operations.
FWIW I found that he has some pretty good deals on his web site-JMO. I am not affiliated in any way with the place.