This is a problematic question since many of those silenced are unknown except to Scientology. No doubt, there are many public, staff, and Sea Org who have been silenced. Family members who were never members have also been silenced.
Sometimes, this silencing occurs after the person first signs a pre written statement renouncing what he or she had said or written earlier, such as L. Ron Hubbard Jr.
Jon Zegel went a step further and recorded a tape (tape #4) of retractions.
Some, such as Marty Rathbun, seem to have quietly agreed to an arrangement, with Scientology Inc., to attack critics of Scientology while writing defenses of Scientology Inc. that would not be out of place in Scientology Inc.'s Freedom Magazine. To be fair, Marty's situation is yet to be definitively determined.
So there are many variations.
The point is there are - realistically - hundreds, possibly thousands, of people who have, through various means, been gagged, or silenced, by Scientology. Many agreed to this under great pressure, and to protect their families.
Often, such people are of high character and were simply caught in a bind.
While some of these agreements have the power of the legal system behind them, others do not and - like "freeloaders' debts" - derive their power only from the person having been deceived.
IMO, if a list of such people could be made it would be startling.
And wouldn't it be wonderful if those silenced could once again speak freely?