I always buy mine at the Mini-Super in Charlestown if I don't feel like driving. But if you don't mind a drive, the pies at Carpenter's Farm in Matunuck are better. I think Highland Farms also still has pies (up on Route 1 in Wakefield) but I've never tried them.
Was just going to post the same. Closer to Charlestown, you could check out Carpenter's Farm in Matunuck. They generally make good pies, although I have not personally tried the blueberry.