I was wondering if someone could give me some ideas on how to derive a Gravity model of international trade under the assumption of monopolistic competition and homothetic preferences using a CES utility function This is expected to be different from Anderson and Van Wincoop 's 2003 model in the following way: van Wincoop dealt with total marchandise trade while in my case I am dealing with Agricultural Products only disaggregated into 217 HS4 products.
Any ideas, links are greatly appreciated.