There is a white faced-black cored PVC. unsure who makes it though. Start asking around...harbor supply, AGFA, Piedmont Plastics....none of my first-line vendors have it like Grimco or N Glantz have it.
The other thing you can always do is take your black PVC, and simply Laminate it with white SAV. We do that some as well when its just too much or not worth the effort of trying to keep the white printheads open.