Hey, DeadCactus, check out
this website. They list a few international rotations, and it looks like most of them are open to students as well as residents. You might also want to try looking at the research that American med tox faculty are doing, and see if anything piques your interest. I know that Steve Bird at UMass has done research on organophosphate poisoning in Sri Lanka. Offhand I can't think of anyone else doing international tox research or clinical work, but maybe BADMD and Daiphon know of some more.