Red Jacket Firearms did it on a Saiga 12 gauge. They catalog the suppressor as #BMF-S-12 for $900 (plus necessary BATFE fees). I remember the question "Why"? The answer was because the customer saw it in a movie (No Country for Old Men) and wanted it. Yes it can be done but............
I believe Hiram Maxium was the first to produce shotgun suppressors back around the turn of the century. There are some good technical manuals on suppressors that could prove valuable on the subject. If I remember correctly, he made a comment that it was for the civilized man who duck hunted. Suppressors were a means to shoot quietly and not annoy the neighbors.