http://www.informatiquebridge.com/iltis/products.htm
Not sure who or where this site is, but they have the extinguishers on there for $120. Seems a little pricey to me, but then again once the vehicle fire starts, I suspect you would empty your wallet for one.
Edited to add: They are in Quebec.
Iltis-Components
(Bridge Computing Inc.)
P.O. Box 18, Sainte-Julie, Québec, J3E 1X5
www.bridgecomputing.com
info@iltis-components.com
T : 450-922-1642
F : 450-922-9705