Hair Loss hair loss

I have one of my two male piggies that is losing hair on his left side around his shoulder area. It is a normal pink skin color, no white flakes, or marks on the skin at all. Was thinking about treating him for mites just to be safe. Not sure what ivermectin to buy or where from. I am also a horse person so not sure if I can buy the horse oral ivermectin and give them that once it is diluted or not. If someone can just help me on where to buy ivermectin and how much to give I'd be greatly appreciated. Thanks so much.