For those of y’all who are willing to spend several hundred dollars for a good suppressor and pay protection money to the criminal ATF to simply possess it, BUT, for whatever reason, do not want to modify a perfectly good firearm to accept a suppressor, this may be an option for you:
Custom Clamp-On Threaded Adapter
Maybe not so easily used on many pistols, but it looks as though it would be quite easily installed on rifles.