They advertise their wares via Tor, an anonymous and decentralized network of websites that exist off the grid and out of sight of Google, Facebook, and conventional web browsers.
And in an effort to keep payment out of sight, transactions all take place with Bitcoin, a digital currency that is similarly decentralized and anonymous.
Whether these guys are legitimate or not, you can use the specialized Tor browser you can find and communicate with them. It's illegal, of course. But here they are.