they're OTC pills. Go to CVS, walgreens, anywhere like that. It's benadryl (diphenhydramine) and cimetidine (tagament is the brand name). cimetidine is crucial for all my benzo indulgences. I try to make my 90 mgs of xanax a month last me as long as I can and those potentiators help out.
Also, if you smoke cigarettes, try not to when you're eating xanax. it makes your body clear it about 50% quicker (I believe, I'm too lazy to look up online the specifics), so keep that in mind
EDIT: sorry I'm barred out and am getting reckless. diPHENYLhydramine. sorry about the misspelling