Can you refer me to websites where sellers and buyers of organic
certified products can advertise  ?  Websites with products from
developing countries would be of particular interest, but there might
not be any so this is not a condition.
  
Purely as an example: A website like  www.leatherline.org  (which has
nothing to do with organic !) is a good example of such a
buyers/sellers platform for advertising.  See its Market Place with
Offers and Demands - in this case for leather products and services.

http://www.greentrade.net/en/default.html
Consultation of the directory is free of charge but I don't think it's
that international.

Vogels