You are able to enter at several Deep Web markets with the only help of URLs, it means next : inpending buyers and merchants are not allowed to join the market until they will gtab an alternative URL from an previously enlisted vendor or buyer.
You can find those at https://darkwebonion.com/, it has updated urls to suggested Dark Web marketplaces. You may follow these alternative URL to register on the sites.
Whenever there are some issues with an access (links don't work), you ought to hang around and check for Deep Web markets URLs. Persist with it, for the reason that some of the markets shut down and open registrations periodically, due to server load.