Quesnay did not have a first hand knowledge of China.  In his 
_Despotisme de la
Chine_, published under the nom de plume M.A. in the Ephemerides 
(March, April,
May and June issues of 1767 you can find it in Oncken and on-line from
gallica.bnf.fr)he acknowledges father Duhalde - who assembled various memoirs
and wrote a history out of them - as his major source but states that he
consulted other authors too.  But I would agree with Michael Perelman that
China was used as a ruse.

Apart from E. Schorer book, HESers may wish to consult Lewis Adams MAVERICK
_Chinese influences upon Quesnay and Turgot_ (a pamphlet from a lecture) (1942)
and _China, a model for Europe_ (2 vols) (1946)and Virgile Pinot (of whom very
little is known) _Physiocrates et la Chine_ (1906) and _La Chine et la
formation de l'esprit philosophique en France (1640-1740)_ (1932, available on
line)

Nicholas J. Theocarakis