Marks in a toilet bowl?

Hi there - Hopefully someone can help me with this.
A plumber used a metal implement to unblock my toilet, and a dark grey marks were left. I thought it might be a scratch and that would need to be repaired, but reading up other people's experiences of this it seems that it might be just a mark which I can remove myself: http://www.finishing.com/193/33.shtml

For this job, everyone seems to recommend a product called Barkeeper's Friend. I've called every hardware store in Dublin and no-one's heard of it - does anyone know where I could get it, in Dublin 2/4/6 hopefully, or something that might do the same job? I'd really appreciate some advice - thanks!