If your from Europe, you can order Ivermectine from this shop:
and search for eqimectin 800.
During the payment process, select pick up by postal service and let the prescription be done by the shop.
It works, I have 6 tubes now, maybe you could also order international, but there's customs coming into play.
Edit: fixed the link.
Each applicator is sufficient to treat 800 kg of body weight. With each weight mark on the applicator plunger, a sufficient amount of paste is dispensed to treat 100 kg of body weight. Loosen the knurled ring by turning it a quarter turn and slide the piston shaft up so that the side of the ring facing the piston is at the height of the prescribed weight mark.
This. Easy for me at 100Kg... :)