US sales of silencers went from 285,000 in 2011 to 360,000 in 2012. According to the ATF there's now a 9 month waiting period for registration approval, and applicants must provide the ATF with a photo and fingerprints, and pay a $200 tax.
The assault rifle buying binge provoked by the Newtown shooting has tapered down, and those same people are getting set up with silencers, flashlights, laser scopes, stocks, pistol grips and rail systems for attaching other accessories.
SOURCE
http://money.cnn.com/2014/04/22/news/companies/gun-silencer-sales/