I got mine from ebay you can bulk order the powder at a good price if you have a scale to weight the dosage. Before that I used a local farm store but it got pricey.
If your catching them early and not having to take the extreme dosage like I did it I would start with 50mg per kg instead of 100mg as I described above and adjust accordingly. I also mix the powder about 8% in vaseline and spread topically over every inch of my skin during the week i cured myself, I did already have some ivermectin mixed in that could have made a difference although it didn't seem to do anything by itself.