You are required to login at certain Dark Web markets with the only help of alternative URLs, what determines the following : new clients and merchants can't enroll until they will get an alternative URL from an already joined customer.
Those can be found at darkwebonion.com/, it has fresh alternative links to concerning Darknet marketplaces. You should follow these alternative link in order to get access to the sites.
In case that there are some issues with an access,for example, links won’t work, you shall hang around and check for Dark Web marketplaces URL. Carry on, as some of the marketplaces may stop and let registrations regularly, due to server load.