Hi Michaela,
Welcome to the UK, and to the forum. I have just bought a LHD Renault 4 F6, in the UK, and today had it MOT'd. The presence of black tape on the headlight lenses in order to avoid dazzle to oncoming traffic did NOT cause it to fail. So don't worry too much about it. I rang my local Renault dealers, Canterbury, Kent, and they claim to have RHD headlights available, but at £50 each. I shall be following Clementines advice for a long term solution.
Tracey