It's not IBC shaped, but my brother's business "The Wine and Hop Shop" gets malt syrup in large sturdy blue plastic cylinders; barrel shaped, but not a full oil-barrel size. They're HDPE or some other sturdy plastic, and of course the contents are good grade. They are thrown away most of the time. They may not work for you because they may be too small to be practical for filling with large equipment. But they're free.
I do think those caged-bubble type containers (what came up when I searched for IBC) are in use in the brewing industry; I think I've seen them in front of YoungBlood. You might enquire at a larger producer like Capital or Wisconsin to see if they toss them after a while. Alt Brewery might have them because they use a lot of sorghum.
Not a direct source, but maybe it's a lead. Good luck.