There are some odd colormorphs out there, I have even seen pics of blue and white and green and white lions but these oddballs are few and far between. The pics I saw were from Japanese aquariums. Also on an oddball fish like that which actually makes it to the US the price is going to be extremely high. A true black and white lion (not just a really dark one) is probably more common than the afore mentioned morphs. Your best bet is to scan around to various vendors and see which are offering black lions(usually volitans, havent seen any non-vols) then physically call them up and confirm that the lion is a true black and white lion(versus the really dark red ones that normally sell as black lions). If the price is high enough to be worth the effort see if they will send a digital pic. I only say that last part because A: its alot of money for a fish that might not meet your expectations and B: If it is a HIGHER THAN NORMAL sale the employees should be willing to go that extra step to make the sale, after all it takes less than five minutes to take a picture of a fish and email it.
Good luck, I hunted for months for a Blackfoot Lion and never found one, even through the oddball vendors I knew of and personal emails to most of them.