I typed "Mark Twain Journal" into a search engine (Netscape Search),
and one of the responses was "SSSL:Bibliogaphy:Journals:Mark Twain
Journal (MTJ)": clickling on it, I found a listing of Mark Twain Journals
by years starting 1967-1968 and going to 1996. I clicked on the year
for Shillingburg's article (1995) and found a brief synopsis. I don't
know whether a more official data base exists (it probably does); this
one is from _Mississippi Quaterly_.
The topic you mention is just the sort of item that MTJ is likely to have
done. When I have the chance, I'll try to find something in one of the
indices (paper) I have received over the years.