Well, I can tell you that we don't have any gun shops anywhere nearby (unless you consider Wal-Mart a gun shop
)! If you are in law enforcement, you can stop by AAA Police Supply (Dedham, next to Cinema complex) on US 1 only ~8 miles North from where you'll be, but if you aren't a LEO they won't have anything of interest to you . . . no black rifles.
Nearest thing is AFS in No. Attleboro, right beside Rte. I-95.
www.americanfirearmsschool.com/You can at least rent something and shoot there (very nice hi-power indoor range). I haven't been there since they started selling firearms and have no idea what they rent (besides pistols).
Best gunshop in the state is 50 miles North of where you'll be
www.fsguns.com and they have the best prices in the area as well. But you'd severely regret the drive back to the Walpole area any time after ~2:30PM as it often is bumper to bumper.