I was hearing on the radio about how Thomas Jefferson wrote to George Washington about his reservations on allowing Massachusetts to become a state because of the extremely religious population.
Whether this was true or not, it got me thinking about all the letters in general that were written to each other in regards to their worries and such on forming a new government.
http://founders.archives.gov/ contains much of the founders correspondence
This book will certainly help, many of them are letters:
You can look inside the book and have a look at the index online to see the addressees, some would be the individuals you are after.
Look for "The Federalist Papers" and "The Anti-Federalist Papers". They are sometimes available in a single volume.