You can find this issue online here: http://www.centerplace.org/history/ts/v2n09.htm
You can also see the entire letter here: https://www.lds.org/ensign/2002/07/the-wentworth-letter?lang=eng.
There's an excellent historical introduction here: http://www.josephsmithpapers.org/paper-summary/church-history-1-march-1842/1#historical-intro
I have a 40-page chapter on the Wentworth Letter in my upcoming book, The Editors: Joseph, William, and Don Carlos Smith. We're going to release it at the conference on April 6.
Here's an excerpt from that chapter:
The Wentworth letter is an amazing accomplishment, and not only because of the Articles of Faith. It is a succinct explanation of the history of the Church and Joseph's own experiences.
Where you can't see the entire letter is in the lesson manual Teachings of the Presidents of the Church: Joseph Smith. The reason: the manual edited the Wentworth letter to omit Joseph's explanation that the Lamanites are the American Indians living in "this country."
I discussed the Wentworth letter here, in the context of Orson Pratt's pamphlet about Church history: http://www.lettervii.com/2016/08/letter-vii-in-histories-volume-1.html