And I've heard that these forms tend to get thrown away - I guess because they don't look like tax forms, or because they are associated with SS? You can get a replacement but it's hassle and time.
Anyway, I believe they're mailed out in January every year, so keep an eye out for them then.
"At times the world can seem an unfriendly and sinister place, but believe us when we say there is much more good in it than bad. All you have to do is look hard enough, and what might seem to be a series of unfortunate events, may in fact be the first steps of a journey." Violet Baudelaire.