One more review of Pudd'nhead:

Saturday Review, 78:722 (Dec. 29, 1894)

I don't have a Norton Critical edition of Puddn'head at hand, but they may
have done some of the leg work for you.  Of course, as Mr. Hirst implied,
there will still be many more reviews out there.  But finding them,
especially in smaller regional papers, will take some work.

You might want to check out one of my absolute favorite reference sources
(not for this query, since I've already checked for you, but for future
queries on Twain and others).  It indexes quite a few of the major journals
from 1870-1910, and has been a lifesaver for me with quite a few obscure
turn-of-the-century authors I'm working on.  Any large library should have
it, I think:

_A Guide to Critical Reviews of United States Fiction, 1870-1910_, compiled
by Clayton L. Eichelberger (Metuchen, NJ: The Scarecrow Press, 1974).  [2
volumes]

Good luck.

Scott Dalrymple
University at Buffalo