I am looking for the letter from Jesse Palmer to S. T. Mason written July 20, 1835. Mason was the Govenor of Michigan Territory. This letter was in the Smithsonian - Schoolcraft papers - File Case A Nol 315. the Smithsonian informed me these papers were turned over to the National Archives. A google search of "jesse palmer to s. t. mason" will find the transcribed letter in Google books.
You might try the Library of Congress which has the Henry Rowe Schoolcraft Papers. You can find their finding aid here:Henry Rowe Schoolcraft Papers: A Finding Aid to the Collection in the Library of Congress which also includes information about contacting them.