You need three things:
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a usenet client for downloading files. I use SABnzbd
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A usenet provider. This is where you are downloading from. I haven't done a huge amount of research here, just grabbed something cheap for now, and I'll explore more later if necessary: Frugal Usenet
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and finally; A usenet Indexer. Equivalent to a torrent indexer like TPB, but for .nzb's and pretty much always paid access. I went with NZBGeek mainly because it was recommended alongside frugal and I didn't feel like digging more at the time.
At $6/mo for those two, I'd say give it a try and explore more/other options as needed.