When I was at a Carpet one store they had a concept board from A and A Global supplies with "Casa Bianca" marble: white with gray veining. At first when I looked for the website it was only in Turkish -- but last night I tried again and behold, it's in English now.

They have these tiles in 3''X8'', 6''X12'', 12''X12'', 8''X18'', 18''X18'' sizes. You may be able to contact them and see if there is a local dealer. It may be whiter than your carrara, but the veining was definately gray, vs. brown.

Rita

Here is a link that might be useful: large marble subway tile source