New black / metal guns are harder to come by right now, particularly pistols. They're out there, but not as plentiful as they used to be. Tons of used guns for great prices though. Just as good IMO.
As for where they come from, it's not from private importation. If you use your search-foo properly, you'll find the answers to where they come from posted at several places across the forums. No specific details, but close enough to know how they get here and end up for sale.