Where are the silence dogood letters located?

The Silence Dogood letters written by Franklin were destroyed by Franklin's brother, who had been deceived by his younger brother in believing the letters had been authored by a widow named Silence Dogood. Upon learning of their true authorship, James Franklin became angry and burned the originals in protest. He could not, however, burn each and every copy of the New England Current, thus we have the original text of the letters, but not the originals themselves. In the film " National Treasure", it appears as if the originals are kept in The Franklin institute in Philadelphia, but a call to the Institute would confirm that, no, they do not have them.