You might try Secret Recipe
or Wedding Night from Joe Ghio
Secret Recipe is a luminata, but luminatas are essentially just plicatas with the colors reversed so it should be OK.
Paul Black mentioned in his catalog that Circle of Light is good for breeding dark plicatas. I've never been able to get anything from it, but haven't tried all that hard either.
Or, speaking of Paul Black, maybe you can talk him into introducing this seedling:
or Keith Keppel into introducing this luminata:
They both looked very nearly black from a distance.
