Tom, not sure how many you need, but if it is just one or two, could you knock them up yourself?
You could have a chat to GJH as they do a fire extinguisher as part of their workshop set.
http://www.gjhplant.co.uk/index.php...category_id=6&option=com_virtuemart&Itemid=55
There are similar items in a JLTRT Mk.1 kit, probably in a Mk.2 kit as well. I may be able to provide an image with appropriate JLTRT reference number in the morrow.