You are allowed to login at distinctive Deep Web marketplaces with the only help of URLs, which suggests a tricky situation : new customers and dealers can't enroll until they will receive an alternative link from an previously joined user.
Look at http://deeponionmarkets.com/, it stores active alternative URL to all of the Darknet marketplaces. You shall follow these urls in order to register on the sites.
Whenever there are some problems with an access (links don't work), you may hang around and check for Deepweb marketplaces links. Keep trying, as long as few marketplaces close and launch registrations frequently, based on server load.

Интересный проект.