Heavy duty shelving rack

You can get purpose made fish tank stands - wrought iron ones. May be look on eBay, Gumtree etc for second hand ones. Google for a brand new one. The only thing to watch though is the bottom tank might be too low for an external filter or to have access to open the lid etc.

For a racking system - have a look at the Big Dug shelving systems and then Google similar ones. They will give you the weight limit per shelf. There are online calculators that will give you the weight of the water etc but you'll need to input the length x height x depth of the tanks.

Water weighs 1kg per Litre, would need hxwxd as you have only supplied 2 measurements