Add an audio clip to the Timeline, then right-click the clip
and set "Audio Gain..." to -999 dB.
Better yet... pre-render an audio file with no content,
name it 'Slug', and import it into this (and future) Projects
to use as a 'silent audio slug'.
This is not built-in, like the Black video clip. You'd have to create your own, but it would not be infinitely expandable like a Black clip. And it would always come into your sequence at whatever duration was set, either in the file or with In/Out points.