I haven't had luck finding big drums but I'm keeping my eye out for a source.
I like making stands using steel tube for a vertical and a hexagonal base. I use something like 2" x 1/4" flats (rectangular bar). Cut six pieces of the bar that are 12" long and weld them in a hex, gives 24" between opposite corners. I weld in three pieces of angle iron from three corners to the tube, and then fill the base with concrete. Obviously wider flats would use more concrete, but typically I end up with 120 lbs of concrete in 24", mounding it up a bit toward the center. I happily throw in any misc mortar or other masonry products. For a clean look a little Bondo can be used to finish the concrete if you want a really nice base.
Obviously you could use concrete to fill in other shapes too, including brake drums, to add mass.