Haven't looked for a while, but it used to be fairly common to be able to find them on both Amazon and eBay, usually listed as "lawnmower mufflers", with pretty un-subtle hints:
"This lawnmower muffler fits a 9mm exhaust and you can bang around your back yard all morning without disturbing your neighbor."
It was a thing for a while, less so now though. To be fair, while they're illegal if fully finished (it's complicated, the ATF changed the rules recently), they're not exactly a threat to anyone. They just make weapons less concealable and only minimally decrease the audio signature. They're not like the movies. Congress and the ATF have been pushing to deregulate them because the paperwork burden required to make/buy them legally is gumming up the works at the ATF and they're unregulated in a lot of the commonwealth/European countries.
Suppressed firearms are still quite loud, typically 120-150dB, vs 145-175dB unsuppressed. It's enough to reduce hearing damage but still sounds like a gunshot.
The sound they make in movies couldn't be further from reality.
1) In most of this country it's entirely legal to own and use a suppressor - so there's plenty out there "in the wild" and few if any are used for crime.
2) These listings are usually predatory BATF Honeypots (designed to catch only the dumbest among us) - but even if they aren't, there's still little if any crime committed with them. So, why even worry?
Is this similar to the brass knuckles, I mean “belt buckles”, they sell in shady gas stations? Or the tobacco shops who sell pipes for anything but tobacco? As long as they don’t say it’s for illegal use it’s a gray area.
I remember the time I was looking shaggy and walking out the door of a supermarket from the wrong direction with a large open-topped bag (and no stolen goods) and the manager of the store, who looked like a detective from a 1970s movie, followed me out on my heels holding a big clipboard which I suspect he would have whacked me with if I'd given him any trouble and later would claim that he was just holding a clipboard and I got hit my mistake.
Not sure why you're being downvoted, that's a legitimate question. The ATF spends a lot of time going after illegal silencers (usually sold as 'oil filters') but they generally focus on end users who buy in quantity or the manufacturers who 3d print them. Have not heard of them going after marketplaces like eBay, but then again marketplaces generally bend over backwards to maintain compliance with firearm regs because they don't want to see a headline like 'mass shooter bought weapons on ebay'.
Other than in Hollywood movies, is there any crime that is enabled with a suppressor that isn't enabled with just the gun itself? Is everyone collectively harmed by one person possessing one?
Lots of gun owners think the rules around suppressors are silly, because the reduction in noise is a huge quality of life improvement for everyone around you -- and a glance at the police blotter in any major city should show that gun crime isn't exactly hindered by the lack of suppressors!
and... most importantly... a suppressed firearm is still not quiet! - and is not hearing-safe to fire indoors!
Hollywood and video games have convinced the population a suppressor is impossible to hear and you can shoot people in public without anyone knowing. Ridiculous, to say the least.
Even then, it's still obvious a gun was fired. The John Wick scene in the subway is so laughably absurd, but so many people think that's what happens when you screw on a can.
More to the point, there's nothing that can be done about thread adapters for oil filters. There are any number of legitimate uses for a 13/16"-16 to 1/2"-28 adapter.
Haven't looked for a while, but it used to be fairly common to be able to find them on both Amazon and eBay, usually listed as "lawnmower mufflers", with pretty un-subtle hints:
"This lawnmower muffler fits a 9mm exhaust and you can bang around your back yard all morning without disturbing your neighbor."