Best way to equalise lighting across the whole card?

I would reshoot also, as that actually might save you more time. If not, I would use a curves adjustment layer with a gradient mask to equalize the image. If the cards are all the same in the way of imbalance, you might be able to just drag the adjustment layer to the other images. The other option would be to bring them into Camera Raw and use the gradient to make the correction, then apply that correct to the rest of the images.