Franklin and Harriet Whitmore's more than 300 letters to Twain are recorded
in Machlis, most preserved at MTP. Twain's more than 400 letters to the
Whitmores are also recorded by Machlis, at various locations. I assume you
can access much of this through the online letters archive at MTP's website.
Most of the books Twain gave to the Whitmores are at MTM. If Whitmore had a
file of Twain papers besides letters, they seem not to have survived --and
I've looked for them.

At the time of Twain's death Whitmore had two oil paintings of Twain, both
done from life by Whitmore himself. One ca. 1885, and one showing Twain in
his old age, possibly painted when Whitmore and his wife visited Twain at
Stormfield (there's a photo of them during this visit, the negative
unflipped). I have some papers describing Whitmore's estate, with no mention
of any Twain papers, but mention of both paintings which went to his heirs.
The 1885 painting showed up in an antique mall (not recognized by the seller
as Twain) and was offered to me for a very low five-figure price. I
declined. It was professionally conserved and went to a local dealer who
priced it $35,000, then to CA dealer at $60,000, and then ended up with a CA
dealer with a $100,000 price tag and a fancy frame. That last dealer put it
up at auction where it failed to sell (the auction house had its catalogues
printed in Europe and they were shipped to the US too late to be mailed out
before the auction). After the auction I bought it, along with a group of
other items that had failed to sell, for substantially less than the price
at which I'd been offered the thing before it began its dizzy climb up the
ladder of dealers. There are many pastels, pencil, gouche, and ink drawings
of Twain from life, but of the 19 oil paintings of Twain done from life,
this is the only one in private hands.

The painting by Whitmore of Twain in his old age has not surfaced (yet).
Hope springs infernal.

Kevin Mac Donnell
Austin TX