I know it's not ideal and doesn't answer your question about availability, but Rifaxmin is available over the counter at the bigger pharmacies in Phnom Penh, Cambodia.
Any reason you specifically want to use this particular antibiotic? SIBO, perhaps? If that's the case, you might want to look at Metronidazole AKA Flagyll. Augmentin may also work. Or consider herbal anti-microbials like Oregano oil / Neem / Allicin. (Oregano oil is far and away the strongest of these, assuming you get one of the better brands like Gaia Herbs or my favourite, North American Herb & Spice.)