I've already posted about the probable Vitelotte I found in the market. I've now discovered a page here: http://www.plantnames.unimelb.edu.au/Sorting/Purple_Congo.html which suggests that this and several other old black potatoes are strains of the same variety. It's going to be a question of growing them out and comparing them. If I can get a crop despite the blight, that is, since it seems to be endemic on the site now, and they're all late maincrops.
Not long ago I found some pink shallot type alliums in the market, which I planted to see what they did. I got the Plants of Distinction catalogue yesterday, and spotted a variety called Pink Torpedo (http://www.plantsofdistinction.co.uk/acatalog/A-Z_of_Vegetables_ONION.html , partway down the page), which looks just like it. If so they'll give me seed this year, and I'm definitely not complaining at that. From what they say, it's mild-tasting European variety.