Yes, there are some legitimate russian ones, and a few mexican, where you can easily find this category just about everywhere and without prescription. Note those will be generic and thus cheap (personally, I have no prob. with this).
If you decide to use a canadian pharmacy, go to CIPA (Canadian International Pharmacy Association) for a list of approved pharmacies, there are plenty, which will always require prescription, although your pills will be expensive and thus high quality, brand name medication.
You are typically looking at Zofran (Ondansetron), Phenergan (Promethazine) and Reglan (Metoclopramide). Unforrunateky I can't guide you as to what the most effective one is, but going by Exit International and Philip Nitschke's occasional recommendations, Metoclopramide is usually mentioned and administered by them; probably also by Pegasos and Dignitas.