Have a look at carseat dot se Ginger.
That's a good site! But they don't have a lot in the way of extended harnessing, they're more about extended rear-facing. I think they only have one seat that forward-faces with the harness, the Britax Two-way I think. They sell European seats and not many forward-face with harness. I just spoke them about this last week. Maybe Securatot in the UK might have more range for FF with harness. I'm not sure but could be worth a look.