>I've searched your site (and others) extensively, but have been unable
>to come up with a quote from Thomas Jefferson that I am quite sure
>exists.  It has to do with political discourse and any attempts to limit
>it (i.e., limit money in campaigns).  Can you steer me in the right
>direction?

I feel quite sure that the topic of campaign contributions was never
addressed by Jefferson, although he did write about the free
communication between citizens and public functionaries.  Most of these
are on my site under "The Right of Free Correspondence," although
some of them are new and are not yet posted to the website (I am just
finishing up going through the 20 vol. set of the Writings).  Below are
several related to this topic.  They all relate to ideas, not money,
although some of the more general statements could possibly be taken
as applying to contributions also.

"The right of our fellow citizens to represent to the public
functionaries their opinion on proceedings interesting to them is
unquestionably a constitutional right, often useful, sometimes
necessary, and will always be respectfully acknowledged by me."
--Thomas Jefferson to the New Haven Committee, 1801.  ME
10:269

"All of our fellow citizens'... safety is passed away whenever their
representatives are placed, in the exercise of their functions,
under the direction and coercion of either of the other
departments of government; and one of their most interesting
rights is lost when that of a free communication of sentiment by
speaking or writing is suppressed." --Thomas Jefferson: Virginia
Petition, 1797.  ME 17:363

"A right of free correspondence between citizen and citizen on
their joint interests, whether public or private and under
whatsoever laws these interests arise (to wit: of the State, of
Congress, of France, Spain, or Turkey), is a natural right; it is not
the gift of any municipal law, either of England, or Virginia, or of
Congress, but in common with all other natural rights, it is one of
the objects for the protection of which society is formed and
municipal laws established." --Thomas Jefferson to James
Monroe, 1797.   ME 9:422

"The right of free correspondence is not claimed under the
Constitution of the United States, nor the laws or treaties derived
from it, but as a natural right, placed originally under the
protection of our municipal laws and retained under the
cognizance of our own courts." --Thomas Jefferson: Virginia
Petition, 1797.  ME 17:361

"For the Judiciary to interpose in the Legislative department
between the constituent and his representative, to control them in
the exercise of their functions or duties towards each other, to
overawe the free correspondence which exists and ought to exist
between them, to dictate what may pass between them and to
punish all others, to put the representative into jeopardy of
criminal prosecution, of vexation, expense and punishment
before the Judiciary if his communications, public or private, do
not exactly square with their ideas of fact or right or with their
designs of wrong, is to put the Legislative department under the
feet of the Judiciary, is to leave us, indeed, the shadow but to
take away the substance of representation, which requires
essentially that the representative be as free as his constituents
would be, that the same interchange of sentiment be lawful
between him and them as would be lawful among themselves
were they in the personal transaction of their own business; is to
do away the influence of the people over the proceedings of their
representatives by excluding from their knowledge by the terror
of punishment, all but such information or misinformation as may
suit their own views." --Thomas Jefferson: Virginia Petition, 1797.
ME 17:359

Hope that helps.  Offhand, that's the best I could do.

Best wishes,

Eyler Coates