maybe you wish to consult  
http://socserv.mcmaster.ca/~econ/ugcm/3ll3/obrien/mediaeval.pdf  
http://www.newadvent.org/cathen/index.html  
and M. Blaug (ed). St. Thomas Aquinas (1225-1274) Elgar 1991   
  
I trust you are familiar with   
http://socserv2.socsci.mcmaster.ca/~econ/ugcm/3ll3/  
http://gallica.bnf.fr  
  
Nicholas J. Theocarakis