You are allowed to access to some amount of Dark Web marketplaces using only the links, this means next : prospective customers and dealers are not allowed to join the market until they will get an alternative link from an already enlisted vendor or buyer.
Search for those at https://darkwebonion.com/, it posts fresh links to all of the Darknet markets. You should follow these links to sign up at the sites.
Whenever there are some issues with an access (links don't work), you should hang around and check for Deep Web marketplaces alternative link. Carry on, because some of the markets shut down and let signing up from time to time, due to server load.