There are ways of doing it. The ones you see in movies are typically hollywood nonsense (I mean come on, how many revolvers have threaded barrles for screwing on a suppressor anyway?), but it is possible.
In order to do it, you have to close the cylinder/barrel gap. The Nagant revolver did this by design when it fired, so suppressing it was of little difficulty (and the anemic 7.62mm Nagant cartridge it fired was subsonic at the muzzle anyways).
In another instance, I believe, a Dan Wesson revolver was used, with the barrel screwed in extra tight to close the cylinder gap.
The big question is, why? Why suppress a revolver when it's so much easier to do it to autos?
Well, there are a few advantages. If you're doing the kind of pistolcraft that calls for a suppressor, then it's probably better if you don't leave spent brass laying around.
Also, revolver cartridges are often more powerful and/or have greater case volume than auto cartridges, allowing a much heavier bullet to be used (if your bullets have to be subsonic, heavier is always better). A 325 grain bullet at 1050 fps (out of a subsonic .45 Colt load) beats a 230 grain bullet at 950 fps (typical .45ACP +P load) any day.
I don't think you can suppress your typical Smith & Wesson or Ruger revolver, though.
(I think having a suppressed revolver would be just bad @$$, but that's me and I'm weird.
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