Surface Pro 512gb availability?

I feel kind of like spending too much money and going for the gusto with the 512gb Surface Pro.

The MS Store's preorder page, though, only lets you preorder the 64/128/256gb models. Does anyone know when the 512gb might be available? Best Buy has preorder available but for some reason I don't really trust them, when the MS Store itself doesn't have it for sale yet.

I kind of think I'm the only person on the internet thinking about buying one of those, because I haven't found anyone else asking.