[egeekuk]

They are in the UK, certainly here in Northern Ireland at least. On the way out of Enniskillen there's an estate with them on it, but you can clearly see the difference between the non-solar and solar tiles in the roof. Here's a couple of products [0] and [1] (I'm not affiliated or connected in any way, just been looking into this while planning my own house).

There's also this stuff [2] but I've never actually seen it installed anywhere yet. It takes a completely different approach and is more like a metal roof than slates.

[0] http://www.solarcentury.com/uk/c21e-tiles-and-slates/

[1] http://www.solexenergy.co.uk/

[2] http://www.viking-house.co.uk/tri-solar-roof.html

(edited for formatting of the references)