Scale can be used for this, the key is the Pivot Point, so just make sure that's set to "Median Point". Or alternatively snap the cursor to the selection centre ("Shift+S" select "Cursor to Selected") then press "." ("Period/FullStop") to use the Cursor as the Pivot (press "," to revert to default). This only really works well however, if selections are symmetrical, especially where more than two elements are selected, as the action is based on averaging the manipulation across all the selected item. This also affects the use of 'axis locks', pressing "X", "Y" or "Z" after engaging Scale to lock motion to their respective axis.
It can also be done to an extent using "Mirror" but that requires the object(s) to be set up that way for it to be useful (you're mirroring across an axis rather than between a selection).