Letter link: Letter from J.R.R. Tolkien to Sterling Lanier • 10 January 1966 (#721)

Image of this letter (and other 6 letters in this group) can be found at https://www.betweenthecovers.com/images/upload/BTC_Catalog_204.pdf

Edit: I didn't realize a better auction link is given in Letter from Edith Tolkien to Sterling Lanier • 11 February 1965 (#587) , which should be inserted for other Lanier letters too.