I have spent a bit of time on line, particularly Ebay, looking for a source for IBCs at a reasonable price, reasonably close by my home, and not contaminated with something nasty. I am planning to build my system on a shoe string, as well as looking for the best use of space in a 4M x 3M Keder house, and I reckon I can use an IBC for the fish tank, a plastic water tank for the sump (planted in the ground and packed in insulation sheets) and five second-hand bath tubs for grow-beds. The sump will be covered so that it can be walked on, thus saving space.
But as for the IBCs, I got sick of looking! I was talking to a friend of mine who processes organic food, and mentioned my frustration - whereupon he said that he gets them all the time, and that his have only been used for sunflower oil. And they are only 5 miles away!
I spoke to my son about all this, and he told me that our local all-purpose hardware store also stocks them, quite cheap!
We are inclined, these days, to assume that the internet provides us with all the answers. Perhaps if we looked closer to home at the outset, fewer small businesses would be going out of business!