This company sells them: http://www.somersetlevels.co.uk
When you get the website, type into the Search Box either: Product Code W1825 or the word "trolley" and you will see it.

I think this is what you are looking for. The company does say "Delivery UK only" - but if, as you say, you are wanting to place a larger order, you may be able to get them to the US. Worth a try.

In the UK, they are generally known as "baskets on wheels" if you are wanting to search further.

Cheers,
- jeanie