Grid Layout for category items

Hi

I have looked at GridMarket for the grid layout that I would like to achieve but I don't want to override my existing theme. To explain further my site has the Weaver II theme running and the store/shop (with MarketPress Plugin) is one menu and subsequent pages within this theme.

I have seen the MarketPress Product Grid Shortcode which works for the main Products page only.

Has anyone developed something similar for the Categories page?