What is the origin of the term "wheels of commerce"?  In particular,
I'd like to know when the term was coined.

bie-ga,

The phrase makes its first appearance in 1735:


George Berkeley
The querist, containing several queries, proposed to the consideration
of the public.
Dublin, 1735


You can see the full text of The Querist here:


http://socserv2.mcmaster.ca/~econ/ugcm/3ll3/berkeley/querist
...461 Whether to oil the wheels of commerce be not a common
benefit? And whether this be not done by avoiding fractions and
multiplying small silver?


Almost all English language publications from the 1700's and earlier
are available in various online databases, which I searched for any
earlier uses of the phrase, but none turned up.  Ol' George appears to
have been the first to put it in print.

Let me know if there's anything else you need on this.


pafalafa-ga