Who are some of the japanese print artists who depicted images of the
story of the 47 ronin in the early 1700s?  particularly those before
the censorship imposed by the tokugawa government?

A variety of search combinations of chushingura and ukiyoe
result in some hits...but most of the prints seem to be from
the mid-1800's and perhaps influenced more by the play
than the actual incident.  (I am not an expert)
Keisai Eisen is one name which does seem to stand out, though.

Amazon.com has an out-of-stock book :
Chushingura and the Floating World: 
The Representation of Kanadehon Chushingura 
in Ukiyo-E Prints (Japan Library)
ISBN : 190335000X

Also...might be totally unrelated, but you might consider
contacting John Carpenter of the Sainsbury Institute.
http://www.sainsbury-institute.org/carpenter.html
(seems to be an ukiyo-e expert)

The reason I mention this person's name is because of
this link : http://www.columbia.edu/~hds2/47ronin.htm
{See Note #1 at the bottom of the page...John might
be the true expert you seek)

Good luck,

John's e-mail appears to be :
j.carpenter@sainsbury-institute.org