You don't even need the darknet; there are plenty of clearnet carding forums. Just search "carding forums" — they're right there, hanging about in the open, all Google-visible and everything. (There are dark-web ones, too, but they're not really any different than the clearnet ones.)
From a few cursory searches, it seems like 1. people generally build their own skimming tools by following guides; and 2. this isn't organized crime, but usually just some really obsessive individuals thinking they can get rich quick.
(If you think about it, the incentives for selling the skimming tools themselves are all wrong: if someone with sloppy OpSec buys your tool and uses it, and it gets into the bank's hands to be studied, they've now ruined it for all your other customers.)
From a few cursory searches, it seems like 1. people generally build their own skimming tools by following guides; and 2. this isn't organized crime, but usually just some really obsessive individuals thinking they can get rich quick.
(If you think about it, the incentives for selling the skimming tools themselves are all wrong: if someone with sloppy OpSec buys your tool and uses it, and it gets into the bank's hands to be studied, they've now ruined it for all your other customers.)