You're talking about the sites like Silk Road, right? They're not networked though.
Discussion
Well they have been and partly still are on the Tor network.
Tor is often called the darknet. That's why the markets are called DNMs. DarkNet Market. Did you not see this: nostr:nevent1qqsppv0e09ncse8v2rdpgm9h975z4hrgeffzz9e5pl2e7zfuyv7mtlcpzemhxue69uhky6t5vdhkjmn9wgh8xmmrd9skcq3qyu7h0k3sqf065d37gzmpz4d0eq7ehamtw75n0s3n2lelmyhctt9qxpqqqqqqzl2hemf