Check scrapyards and such, the last thing you want to do is try to cut open a freshly-emptied tank with any possible fumes in it. We had a high school shop class fatality not long ago here. Please be careful... and these might not be food grade. You never know what might leach into your wine from anything metal, especially with how acidic things get. I know you can get stainless steel stock pots quite commonly up to about 3 gallons, and I've seen them bigger, that might be a safer alternative even if not quite as accurate.