Matrox once made a dual-ADC card. It was released within the first year of when Apple started the ADC stuff.
It had HD power connector(s) on the card, the power requirements to drive two monitors is the main reason why a dual-ADC card is impractical.
As for that dual-ADC Matrox card, you guessed it already. No Mac drivers. It was strictly for Windows users who wanted to use dual Apple monitors without buying a Mac.
It also seems to be no longer available. Couldn't find a hint of it on Matrox's site, and it's been gone long enough that Google search is finding nothing useful. Instead, they're offering a card with a dual-link DVI port to drive the modern Apple 30". You guessed it already, no Mac drivers on this one either.