Just my 2 pennies worth, yes Richard has lots of nice nibs and has quite a selection of extra fine nibs but don't make the same mistake I made.
I couldn't find anyone who carried extra fine nibs either so I visited Richards site and bought several Pelikan brand extra fine nibs. I got them, tried and inked one of them and was amazed at how smooth it wrote. I discussed the find with several friends and most of them warned me not to put a branded nib in one of my pens for sale as some manufacturers really frown on this and some actively protect their products very aggresivly. I liked the Pelikan nibs so well that I actually tried to contact Pelikan on several occasions asking for their permission to use their nibs but never got a reply so can only assume that their silence was a negative response.
Luckily, Richard understood my predicament and let me return the unused nibs, except for one that I kept for myself..... man that nib writes so smooth for being as fine as it is.