Thanks to Will Friedwald for pointing this out — courtesy of “Letters of Note” (http://www.lettersofnote.com/search?updated-max=2010-09-28T14:18:00%2B01:00&max-results=6). (Will told me that Nancy Franklin of THE NEW YORKER brought it to his attention, so thanks, Nancy!)
The original source was a Sotheby’s auction (http://www.sothebys.com/app/live/lot/LotDetail.jsp?lot_id=47TQW) where this and four other latters to the singer Gina Gardner sold for £1440.
‘Yea Man’ . . . . . . . . !