I haven't come across a central repository of photos, but if you image search for specific fishing ports and "1920", you'll come up with a variety of helpful photos, postcards on EBay, and whatnot.
The primary fishing ports here in Massachusetts were New Bedford, Salem, and Beverly. For Rhode Island there is Galilee, a village within the town of Naragansett.
The old run-down buildings in those cities now were relatively new and fancy in the 20s. Between the ports, processing plants, and other mills, they were pretty bustling places. Street trolleys for the major public transportation.
Boston & Maine railroad stations up here in Mass; Narragansett Pier Railroad Company specifically serving the industry down there.
If you want a smaller town look, Newburyport Mass had some very ramshackle clam shacks for the shellfish industry, and I'm sure the workers there would have frightened Mr. Lovecraft.