Hi! The ivermectin is a thickish liquid (it's sold as injectable for farm animals) and you use it topically. Look on line, amazon has a few places resourced. Get the dark brown box with the steer head on it.
If you know someone at a pet pharmacy (or any pharmacy that makes drugs for animals) you can ask for a cream to be made up: neutral cream and ivermectin powder (which they have; it's quite common).