As explained in this article from my hometown newspaper, the American Radio Archives and Museum is a "a still-growing collection [of radio broadcasts] that began in 1984 and now boasts some 30,000 audio recordings, 40,000 scripts and 150,000 photographs." It's especially focused on the "Golden Age" of radio from the 30s and 40s, before television became dominant, and is "one of the largest radio broadcasting collections in the world."