Check on Craigslist in the free section of your location and you might find some free metal barrels.
I found 2 free metal barrels on Craigslist last year that were just a few miles away from my home.
Although if you can't find free ones you can usually buy them pretty cheap on Craigslist too as I've seen some go for $5.00 to $10.00 a piece which is really cheap.