I've been using one of these Rubbermaid carts for about 3 years. Hope one of this link will work for you:
http://www.reviews.bonsaitalk.com/c...ails&itemid=279
I have seen them on retail at Orchard Supply Hardware, too. I made a plywood turntable that fits right into the recess where the soil grid/repotting tray go.
Regards,
Matt