You could also cut them from a block of cast iron, the chests on my 2″ Fowler are cast integral to CI the cylinder but if I were making something like a 2″ Minnie where they are separate I would do them in iron, same for the covers..
Most of the stationary steam engines that I make I also cut the chests from iron, either rectangular bar or square up a slice cut from round bar depending on what fits and what I have to hand.