[Mithadan]

I tend to agree with Elenhin. The palantiri's primary use was communication (or intelligence gathering). If they existed and had such a purpose, why lock them away. They were likely distributed to various people/places and none (or maybe just one, a large stone) was in Formenos.

There were only 7 given to the Faithful. One more was apparently kept in Tol Eressea. There may have been others.

We don't know when the palantiri were given to the Faithful. Perhaps they were given to the royal family and passed on to the faithful like the Ring of Barahir.