You are allowed to login at several Deep Web marketplaces with the only help of links, that determines next : new buyers and dealers are not allowed to enroll until they will receive an alternative link from an already enlisted customer.
You can find those at httр://deeponionmarkets.cоm/, it posts active alternative URLs to all of the Deep Web markets. You shall follow these urls in order to register on the sites.
Wherever there are some issues with an access (links don't work), you ought to lie in wait and check for Darknet marketplaces URLs. Keep trying, because some of the marketplaces shut down and open signing up frequently, due to server load.