Retailers report a surge in sales of gun silencers since the start of the year, a trend attributed to a forthcoming Obama administration regulation expected to create roadblocks for the most popular way of buying the devices.

Luis Rose, owner of Sterling Arsenal, a gun shop and manufacturer in Sterling, Va., said that by the end of January, he has sold half the year’s inventory of one of the most popular silencer brands. Mr. Rose said he typically sells about $100,000 of those silencers a month, but so far has sold about six...