Where do you find information on a riverside arms model 520 pump shotgun?

You can find information on a Riverside Arms Model 520 pump shotgun by checking firearms reference books, online gun forums, and websites dedicated to firearms history and collectors. Additionally, visiting sites like GunBroker or ArmsList may provide listings and discussions about the model. You might also find useful information on YouTube, where enthusiasts often post reviews and details about vintage shotguns. For historical and technical details, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) may have resources as well.