HID conversion kits on EBAY
that is a place to start...
it is really hard to find specific vehicle conversion kits, as far as I know there is no HID available on the stock Titans, and I am not sure if the reflecting surface is parabolic enough to properly use HIDs.
oh and if you are going to purchase them... I reccomend 4700K...
while the higher Ks are brighter... they also have more color... and do not provide the same ammount of reflection back to the driver...
trust me on this one... having owned 4700K - 10000K (insane purple color) the 4700's put better light on the road... much easier to see...