Are you implementing each card by hand? I was going to make something like this and was just going to regex match all of the cards (from HearthPwn). It seemed like there were few enough variations to make something like that possible.
A lot of the cards are more or less automatically generated in the sense that they don't actually extend any functionality of the parent class. Variations in the special effects ("text" effects) are big enough that for those, I find implementing them one by one much easier.
Curious if you already tried automating it.