This is what I've been using for a few years Nature's Oil USP Kosher Vegetable Glycerin Gallon - 10 lbs https://www.amazon.com/dp/B00WUPUYCC/ref=cm_sw_r_cp_apa_8P8GBbXX7YQN5

You can also buy it directly from their website but Amazon's 2 day shipping makes Amazon a better deal.