I figured you might have them from fertilizer, which would be good for watering garden. We get 'white oil' in them at work, but they go back for refill. That stuff is USDA approved for food contact. Wouldn't be afraid to use some thing like that.
For some reason, finding the Food grade ones within driving range is nearly impossible. I can find plenty of food grade 55 gal drums. There’s a local meat processing plant that sells them after they empty them of their salts, seasonings etc.