The cover that I posted in this thread with the Providence RI Control Mark will be offered by Robert A. Siegel Auction Galleries,
in their United States and CSA Postal History sale # 1191, October 25th, 2018. lot # 2383. In this lot they included several interesting covers from the Metcalf/Hunt Correspondence.
Edit; I have communicated with Charles DiComo Phd. regarding this sale.
Also a cover with letter both on mourning stationary, President James A.Garfield's widow Lucretia R. Garfield, on March 7th, 1882, after her husband the Presedant was assassinated, wrote this letter to my great, great, grandfather Levi L. Burdon. This cover contaians a letter of thanks to the " Fifth Rhode Island and Battery Veterans Association" for a tribute plaque that the Association had sent.
The cover and letter can be viewed best on this thread. My post 2/12/16 on this thread
https://goscf.com/t/21923&whichpage=2 