A decade ago, when Spotify was two years old in the UK and had just become available in the US, Chris Johnson started a musical discovery project called TAPEFEAR. He "created a script to find new music on niche music sites, cross reference Spotify to see if it was available to stream," according to a Reddit post, and besides a bit of occasional tinkering, he largely forgot about it. In total, Johnson says the script ran for a decade amassing 42,000 songs.
You can check out TAPEFEAR here. When the random songs appear, you can select "random preview" for a sample or "play on Spotify" to add to your Spotify playlist. If you like it, you can add it to "saved" and curate your favorite niche songs.