TCG Letter #492

Sotheby's Valuable Printed Books and Manuscripts December 2001, Lot. 554 (pp. 264-5)

This letter, along with three others, were sold on Sotheby's in the early 2000s but I no longer have that link, which is suspected long dead.

Sotheby's catalogue details

The J.R.R. Tolkien Companion and Guide - Chronology (2017), p. 627