That's odd. A quick look at sci-hub shows a bunch of ivermectin papers that don't look half bad.
I figure that if a physician wants to go off-label on a prescription they should go ahead. Plenty of warnings of course.
Buying it at the feed store along with fish antibiotics is sketchy, but remember that it's your body after all. People forget that. God knows how many people are harmed by Tylenol overdoses.