Does white chocolate HAVE to have milk in it?
White chocolate by regulation is at least 3.5% milk fat and 14% milk solids. As far as I know, the EU uses the same definition as the FDA (US).

So, nothing vegan can legally be sold as "white chocolate".

That said, there are a great many non-dairy white chocolate substitutes, usually made with any combination of soy milk, maltodextrin, vanilla, and saturated/hydrogenated fat (palm oil, shortening, etc.), among other ingredients/additives of course.

They don't taste the same as real white chocolate, but then again, white chocolate isn't real chocolate to begin with, so it can't hurt to experiment with some of the products out there - which can be easily sourced with a Google search, as one of the comments indicates.