Tractor Supply store, Southern States, RuralKing… if you have any of those in your area. Livestock laxative is the high grade or you might find low grade (not for livestock, but the same thing) in the paints and lubricants.
I eliminated a huge variety of many other preservatives, lubricants, and WD40… use it on everything and more importantly anything. Woods, metals, and nontoxic.