It's way easier to make them than the article describes.
Files and blueprints can be found online, using a VPN or TOR if not in a country that allows blueprints to be shared. Online companies sell the non-plastic component kits needed to complete the weapons if people don't have access to or the tools needed to make them. There are even companies that offer ghost ID's and mailing addresses that redirect to a purchaser. Tack on a privacy based cryptocurrency and it'd be pretty damn hard to track down who's making and using these weapons.