Guys I get my cubes from a local wine retailer. Most wine companies use them to transport sherry, port, and other wines which the retailers then place in large oak barells for sale to customers by the bottle.
So if you have a wine retailer in your area best bet is to ask them for a few. They gladly give them away here in wagga.
They're the same plastic, cubes that have been used for chemical storage? We go through a heap of those at work and I was thinking of taking one of the ones that had contained phos-based cleaners/sanitisers but wasn't sure if it was still food grade plastic.
Some industrial chemical companies sell 25 lt. drums of DI water. They are semi transparent (like fermenters), have a threaded tap hole with bung, and about 50mm diameter screw top and handle.
Also found that Subway throw out used 25 lt. white buckets with lids. They get dill cucumbers in them. It's a matter of getting rid of the smell. The press on lid seals well. They often wreck the lids taking them off with a screwdriver.