NICE INEXPENSIVE GATE
For some reasons, stand-alone gates have become rare. These days gates typically come bundled in a channel strip, but Behringer still makes a 4-channel simple gate. It's quiet and fast, and costs less than any other gate I could find.
One quirk worth pointing out--to make the first channel functional, you have to link all the channels together. This is not the default setting, and isn't mentioned in the manual--I discovered it by trial and error