They should have them for the SL. In fact, I'm pretty sure they definitely have them and that it was from a photograph of a SL that I first got the idea.
I was at the Goodwood Festival of Speed this weekend (checkout
http://www.goodwood.co.uk and navigate the motorsport menu), the theme was 100 years of Mercedes-Benz. In the MB tent was a SL500 "Silver Arrow" which has illuminated door sill plates with a special design.
I have to say, they look great at night, really worth every penny. On Firday and Saturday nights I stayed at my club in St James's Square in London. Pulling up outside and opening the door gave me the greatest pleasure... if only it was a SL and not a humble C...