Caches of MANPADS have been smuggled in to the US for years. Odds are that some morning we will wake up and see commercial airliners failing out of the sky by an air port near you.
The odds are that they have already tried with SA-7s and early SA18s that just dont work, or the plane leaves the target envelope before the missile falls out of the sky. I wouldn't doubt if there has been one or two attempts. Most likely, the missle never lit off....which is endemic in Soviet-era MANPADS...that is why their armed forces volley fired them in the dozens...hoping one would hit.