Why get unusual when the usual sources work just fine? Newspapers, magazines, books of the period, etc.
Id say newspapers and magazines are the best resources. Youll find everything you need to know there--vital stats, fashion, trends, ephemera, crime, politics, attitudes, social issues, everything. There are plenty of old newspaper archives online, and google books has lots of old magazines and books, including old slang dictionaries, manuals, catalogues, maps, travelogues, etc. Ive found tons of obscure info this way. Manuals for pharmacists that let me know what people were drinking at soda fountains, catalogues for news sellers that listed all the various magazines that were available, police manuals that detailed how the police in a given city operated, books about racial issues, social issues, prostitution, driving magazines that listed various types of wagons and their features, vital stats for various cities, you name it. Its all out there.
For pictures and other visual reference stuff you can try the library system for the city your story is set in. Many libraries keep photo archives of their city's history, including old maps. If youre lucky theyve digitized them and have them online.