Maybe it's not open anymore, but I've always enjoyed Kenmore Collectibles - about 7-8 blocks from Fenway. It's been two years since I was there, but here is a thread I posted at the time (June 2012). I bought a very nice T205 Mathewson at Kenmore and took it on the field and in the visitors dugout - 100 years after Matty had pitched in the World Series there.
Here's a link that thread (hopefully I've posted it correctly):
http://www.net54baseball.com/showthr...ghlight=Fenway