I found Bromfield Pen Shop (Downtown Crossing). Looks interesting. Do you know it?
https://www.bromfieldpenshop.com/
Well I just came back from Boston. Cool trip, great city!
For the record, I checked out BPS (just a few seconds near the Granary Burial Ground off the Freedom Trail, so not a major detour) and it's a small quaint shop with a lot of fountain pens and ink and a couple of pointed pen nibs (Brause and Speedball) dueling it out in the back
So I came out of there empty handed but that is not to say you ought not check it out. So it's still PIA and John Neal online, no surprise. Which is too bad, because to me online shopping will never beat the cheap thrill of a real brick-and-mortar shop. Anyway.
I also spotted two Dick Blick's, one on Mass Ave. right at Central T station in Cambridge, and the other near Fenway Park on Brookline near the Regal cinemas.