Okaaaay - possibly not quite the style you were looking for, but
ebay.com (the US site) has a few hits for very wide boots - though
mostly cowboy boots(!):

http://clothing.search.ebay.com/HH_M...Z1QQsofocusZbs

Remember add +1 to your UK shoe size to get the equivalent US size
(widths are the same I believe).

You might email 1 or 2 of the suppliers to see if they do safety shoes/
boots - I'd be surprised if there isn't a supplier somewhere in the
"the big country".

Another option might be military boots suppliers (e.g http://www.silvermans.co.uk/
in London).