funny... I just posted the same exact thing yesterday. Only one person responded. My advice, if you're willing to travel, is to go to the Hassidic part of Williamsburg and hit up all the markets in that area.
Do you mean coke that is kosher for passover with the yellow cap? I would go to the stores now and try to stock up as they may still have some. I think they only produce it for passover. See the link below for more information.