Thanks for the tip. We don't get wheelsmith stuff here, but I have a bunch of Alpina nipples that if I remember correctly are 12mm and 14mm, so I could try them in a pinch.

After all this, I think I've found the one shop in the city that will suffer the extreme inconvenience of having to sell its customer what he wants. Let's see if this friendliness transfers from the phone to a face-to-face encounter. Fingers (3) crossed.