You can also look in a farm supply store. You could use 1 or 2 big ones instead of many smaller ones. They have containers of all sizes, up to like 50 gallon.

I saw a set up like this in a hydro store. The res must have been 50 gallons, with a power head pump circulating the nutes. It had no top, so I guess if you keep them circulating you don't get algea.