The black market, on both survival and skyblock is supposed to be a challenge to find and to get into. As with all black markets they are supposed to be hidden.
Telling other players where it is is pointless, they may as well put the items in the normal market.
Making it easy to get into is also pointless, they also may as well put the items in the normal market.
Come on guys, stop wanting everything handed to you and work on finding things, practice the timings of getting in. It does work.