Colorite is the only place that I have seen advertised as supplying matching factory colors. Their price is $ 86.95 for 1/2 pint of base, $ 86.95 for 1/2 pint of color, and $ 39.95 for a pint of clear....$ 213.85 plus shipping.
http://www.colorrite.com/index.cfm?killnav=1You might be able to find the colors at a good paint supplier for the automotive body shop industry......I am not sure. The local one here is very good at matching solid colors - it is much tougher with pearls, candies and metallics.
You could watch ebay for a tank to come up in the correct color....or maybe it is time for you to get a custom paint scheme done.