Riva:
If you want to fade individual LED's then 4x WS2803 chips will drive 72 LED's (18 LED's per chip).
Where do you even find these? I put WS2803 into Digikey, Findchips, and Jameco and no one seems to have ever heard of them.
I'd go with tlc5940 16-channel PWM drivers. Everyone uses them and there are libraries already written.