This is what you'll be looking for:
http://www.gp-web.com/en/productspop.php?pid=1918
Zero One doesn't have it I just checked.
Firesupport Stocks them but they're out of stock, so I guess they would be the easiest to call up and see if they can include one in their next order/shipment.
http://www.fire-support.co.uk/catego....y=7&submit=Go