Hi Keri, Sorry that happened to you. I tried to go via that link again and it wouldn't work for me either. I got "this page cannot be found." I had it bookmarked.I tried again, just now, to go the home page via, http://www.nationalgallery.org.uk/http://www.nationalgallery.org.uk/
I went on the 'search the collection' and it came up 'no results.' This is very strange as I know I looked at his portrait. It had a section too where one could buy different size reproductions of the painting in different forms( different qualities) with a price list. Maybe an E mail to the Gallery might produce an explanation of what happened to poor James.
I know there are a couple of paintings of him around. I once saw one of him in a BBC (I think) production about the canals and the period. It was in a private house, I believe. It seemed to be a largish portrait, (oil painting) of him. Perhaps that one is the origin of the engravings one sees here and there. Engravings were often the way, before photography, that enabled people to have copies of an art work.If I find the portrait elsewhere I will post again. Maybe someone else knows of a portrait of him that is available on line? Good luck! :-))