How to show available sizes on Atlantic theme product collections?

[Steranko]

Hi there, we're currently using Atlantic theme and there's a small change we want to make to our theme. Basically, we would like it so that when customers are scrolling through our collections on steranko.co.uk to be able to see on each product what sizes are available and which are sold out without them having to click on the product itself. 

Is there an app that would do this for us or some simple coding? Simple being the operative word!!

Thanks