Dear Hemanshu Segal,
The transaction which you are referring is merchanting trade i.e. goods moving from outside India to a place outside India based upon a supplier in India.
Under GST, it is outside the purview of the same. Refer sl.no.7 of Schedule III of CGST Act.
However, for merchanting trade you have refer the RBI guidelines and FEMA for the repatriation, flow of fund and documents.
In case of documentation, in general, A would ask the transporter to supply to B from the place of business of C / the place where delivers to the control of A. If C is directly supplying to B, then there would be exposure to the margin of A to C. These decisions has to be taken by management based upon their strategies and law applicable in such foreign lands.